Ответ весьма важен.

In Russian, the verb to be is usually omitted in the present tense.

So:

• Ответ весьма важен. = The answer is very important.

There is no present-tense is written or spoken here. This is completely normal in Russian.

Compare:

• Ответ важен. = The answer is important.
• Ответ был важен. = The answer was important.
• Ответ будет важен. = The answer will be important.

In the past and future, forms of быть do appear, but in the present they usually do not.

Важен is the short form of the adjective важный.

Russian often uses the short form of adjectives when the adjective is the main predicate of the sentence, especially in sentences like X is important, X is ready, X is necessary, and so on.

So:

• Ответ важен. = The answer is important.

This is more natural than:

• Ответ важный.

The full form важный is usually used more like a regular descriptive adjective before a noun, or when describing a characteristic in a slightly different way:

• важный ответ = an important answer

A useful rule of thumb:

• важный = full form, often attributive
• важен = short form, often predicative

Also, важен agrees with ответ, which is masculine singular.

Весьма is an adverb meaning very, quite, rather, or highly, depending on context.

In this sentence:

• весьма важен = very important / quite important

Compared with очень, весьма sounds a bit more formal, bookish, or elevated.

For example:

• Ответ очень важен. = neutral, everyday
• Ответ весьма важен. = a bit more formal or polished

So the learner should recognize весьма as a common intensifier, but with a slightly more formal tone than очень.

Ответ is in the nominative singular.

It is the subject of the sentence:

• ответ = answer

The adjective важен agrees with it in gender and number:

• ответ is masculine singular
• therefore the short-form adjective is важен

If the subject changed, the short form would change too:

• Идея весьма важна. = The idea is very important.
  (идея is feminine)
• Письмо весьма важно. = The letter is very important.
  (письмо is neuter)
• Ответы весьма важны. = The answers are very important.
  (plural)

No, Russian word order is fairly flexible.

Ответ весьма важен is a neutral, natural order.

But other orders are possible, with different emphasis:

• Ответ весьма важен. = neutral statement
• Весьма важен ответ. = emphasizes important
• Важен ответ. = can sound more contrastive, like It is the answer that is important
• Ответ важен весьма = possible in poetry or special style, but not normal everyday prose

So the basic sentence is not just grammatical; it is also the most straightforward and neutral version.

Russian does not have articles.

So ответ can mean:

• the answer
• an answer

The exact meaning depends on context.

In a sentence like Ответ весьма важен, English often uses the answer if a specific answer is already known from context. But Russian does not need a separate word for that.

This is something English speakers have to get used to: Russian leaves definiteness and indefiniteness to context.

Yes. That is probably the most common substitution:

• Ответ очень важен.

This means essentially the same thing and sounds more everyday and conversational.

Roughly:

• очень = the most common, neutral very
• весьма = also very/quite, but more formal or literary

So both are correct, but they give slightly different stylistic impressions.

The stress is:

• отве́т
• весьма́
• ва́жен

So the sentence is pronounced approximately:

• at-VYET vyes-MA VA-zhen

A more careful approximation:

• [ɐtˈvʲet vʲɪsʲˈma ˈvaʐɨn]

A couple of helpful pronunciation notes:

• In отве́т, the stress is on the second syllable.
• In весьма́, the stress is on the final syllable.
• In ва́жен, the stress is on the first syllable.
• The ж in важен sounds like the s in measure.

Yes, slightly.

The main reason is весьма. The sentence itself is simple and natural, but весьма gives it a more formal or polished tone than everyday speech often has.

So:

• Ответ весьма важен. = correct, natural, slightly formal
• Ответ очень важен. = correct, natural, more neutral/everyday

If you see весьма in writing, news, essays, formal speech, or literature, that is very normal. In casual conversation, очень is often more likely.