Mater dicit unam stolam sex sestertiis constare.

Because this sentence uses indirect statement after dicit.

In Latin, after verbs like dicit (says), the thing being said is often expressed with:

• an accusative subject
• plus an infinitive

So:

• direct statement: Una stola sex sestertiis constat = One stola costs six sesterces
• indirect statement: Mater dicit unam stolam sex sestertiis constare = Mother says that one stola costs six sesterces

In the indirect statement, unam stolam is the subject of constare, but it has to go into the accusative because that is how Latin builds this construction.

For the same reason: this is an indirect statement.

In a normal direct statement, you would say:

• Una stola sex sestertiis constat

But after dicit, Latin changes the finite verb into an infinitive:

• constat becomes constare

So constare is the infinitive meaning to cost.

Because in an indirect statement, the accusative noun is usually the subject of the infinitive, not the direct object of the main verb.

Here:

• Mater = the subject of dicit
• dicit = the main verb
• unam stolam sex sestertiis constare = the whole thing being said

Within that clause:

• unam stolam is the subject of constare

A good test is to turn it back into a direct statement:

• Una stola sex sestertiis constat

That shows clearly that una stola is the subject.

Because Latin usually does not use a separate word like English that in this kind of sentence.

Instead, Latin uses the accusative + infinitive construction to express what English often says with that.

So English says:

• Mother says that one stola costs six sesterces

Latin says:

• Mater dicit unam stolam sex sestertiis constare

The idea of that is built into the construction itself.

Because constare takes the ablative to express price.

So Latin says literally something like:

• to cost at six sesterces

That is why sestertiis is in the ablative plural.

So:

• sex = six
• sestertiis = by/at six sesterces in form, though naturally translated for six sesterces

No. Sex is an indeclinable numeral, so it stays sex no matter what its grammatical role is.

What changes is sestertiis, because that noun has to show its case.

So in sex sestertiis:

• sex stays the same
• sestertiis is ablative plural

Here constare means to cost.

It is a standard Latin verb used for stating price. So:

• stola sex sestertiis constat = the stola costs six sesterces

You may also see constare in other contexts with related meanings, but in this sentence the meaning is clearly to cost.

Unam means one and agrees with stolam.

It is:

• feminine
• singular
• accusative

because stolam is feminine singular accusative.

So unam stolam means one stola. Latin often includes unus, una, unum when it wants to emphasize one single item rather than just a noun.

Because Latin has no definite article.

English says:

• the mother
• a mother

Latin usually just says:

• mater

The context tells you whether to understand it as mother, the mother, or sometimes a mother. In this sentence, natural English usually gives Mother or The mother depending on context.

Because its subject is mater, which is singular.

• mater = mother
• dicit = she says

So the verb is third person singular present active indicative.

Latin word order is much freer than English word order.

Putting the infinitive at the end is very normal, especially in an indirect statement. Latin often places the main verb or infinitive later in the clause.

So this order:

• Mater dicit unam stolam sex sestertiis constare

is perfectly natural.

Even though word order is flexible, the case endings tell you what each word is doing.

It would be:

• Una stola sex sestertiis constat.

That is useful because it lets you see how the indirect statement is built:

• una stola becomes unam stolam
• constat becomes constare

after dicit.

So the sentence is a good example of how Latin turns a direct statement into an indirect one.