kono dentaku wo tukaeba, daikin no keisan ga sugu dekimasu.

使えば is the -ba conditional form of 使う (to use).

• 使う → dictionary form
• 使えば → if you use / when you use

So この電卓を使えば means if you use this calculator.

This form often sounds a little like presenting a condition that makes something possible:

• このボタンを押せば、ドアが開きます。
  • If you press this button, the door opens.

In your sentence, it sets up the condition for the second part:

• If you use this calculator, you can quickly calculate the amount due.

Because the two verbs work differently.

1) 電卓を使う

With 使う (to use), the thing being used is the direct object, so it takes を.

• 電卓を使う = use a calculator

2) 計算ができる

With できる (can do / be possible), Japanese often marks the thing that is possible with が.

• 計算ができる = calculation can be done / can do calculations

So the sentence has:

• 電卓を使えば = if you use the calculator
• 計算ができます = the calculation can be done

This is very common with できる.

In Japanese, できる often combines with a verbal noun (a noun that can act like a verb), and 計算 is one of those.

• 計算する = to calculate
• 計算ができる = can calculate / calculation is possible

So both patterns are natural:

• 計算します = I calculate / will calculate
• 計算できます = I can calculate / calculations can be done

In this sentence, 計算がすぐできます emphasizes that the calculation is easy/possible to do quickly.

の connects two nouns.

• 代金 = charge, price, amount due
• 計算 = calculation

So 代金の計算 means:

• calculation of the amount due
• price calculation
• working out the total cost

The particle の often works like:

• of
• apostrophe-s
• a noun modifier

Other examples:

• 日本の車 = Japanese car / car of Japan
• 数学の先生 = math teacher
• 旅行の予定 = travel plans

Here, 代金 describes what kind of calculation it is.

すぐ is an adverb meaning immediately, right away, or quickly depending on context.

It usually goes before the verb or predicate it modifies.

So:

• すぐできます = can do it quickly / can do it right away

In your sentence:

• 代金の計算がすぐできます = you can do the price calculation quickly

That placement is very normal in Japanese.

Yes, those are possible, but the nuance changes slightly.

使えば

This is a straightforward conditional:

• if you use it
• often sounds neutral, explanatory, or instructional

使うと

Often sounds like:

• when you use it
• if you use it, then... It can feel more like a general result.

使ったら

Often sounds a bit more conversational and can mean:

• if you use it
• when you use it

So:

• この電卓を使えば、代金の計算がすぐできます。
  • If you use this calculator, you can quickly calculate the total.
• この電卓を使うと、代金の計算がすぐできます。
  • When/if you use this calculator, the total can be calculated quickly.
• この電卓を使ったら、代金の計算がすぐできます。
  • If you use this calculator, you can calculate the total quickly.

In a textbook sentence like this, 使えば is very natural.

Japanese does not need an explicit topic in every sentence.

Here, the sentence is fine without は because it is simply stating a condition and a result:

• この電卓を使えば、代金の計算がすぐできます。

The topic is understood from context. Depending on the situation, it could be:

• you
• we
• the staff
• one

If you added は, the nuance would change depending on where it appears. For example:

• この電卓を使えば、代金の計算はすぐできます。
  • As for calculating the amount due, that can be done quickly.
  • This adds contrast or emphasis.

The original sentence is more neutral and natural.

The comma separates the conditional part from the main result:

• この電卓を使えば、 = if you use this calculator,
• 代金の計算がすぐできます。 = you can quickly calculate the amount due.

In Japanese, commas are somewhat flexible, but this one makes the sentence easier to read. It is especially common after a longer introductory phrase like a condition, time phrase, or clause.

So the comma is not absolutely required every time, but it is very natural here.

These words are related, but not the same.

代金

The amount to be paid; the charge; the billable amount. This fits very well in commercial or transactional situations.

• 代金を払う = pay the amount due

値段

The price of an item. This is more like the listed or stated price.

• この商品の値段 = the price of this product

お金

Money in general.

• お金がない = I don't have money

So 代金の計算 is more specific than お金の計算 and often more appropriate in a store, restaurant, or checkout context.

Because it is polite standard Japanese.

• できます is the polite form of できる
• 使えば stays the same regardless of politeness, because the politeness is shown at the end of the sentence

So the plain-style version would be:

• この電卓を使えば、代金の計算がすぐできる。

And the polite version is:

• この電卓を使えば、代金の計算がすぐできます。

This is very common: the final verb shows the overall politeness level.

No. Normal Japanese is usually written without spaces.

So this sentence would normally appear as:

この電卓を使えば、代金の計算がすぐできます。

Textbooks often add spaces to help beginners see the word boundaries. That is only a learning aid.

For example:

• textbook style: この　電卓　を　使えば、　代金　の　計算　が　すぐ　できます。
• normal writing: この電卓を使えば、代金の計算がすぐできます。