Learn Finnish: Kirjat maksavat yhteensä noin neljäkymmentäviisi euroa. - The books cost about forty-five euros in total.

In Finnish, whenever you have a number greater than one, the noun that follows it must be in the partitive singular form. That's why the number neljäkymmentäviisi is followed by euroa instead of the basic dictionary word euro.

How do you build a long number word like neljäkymmentäviisi?

Finnish numbers are built by gluing smaller number words together into one single word. This one breaks down into neljä (four) + kymmentä (the partitive form of ten) + viisi (five). It literally translates to 'four tens five'!

Why does the verb maksavat end in -vat?

The base verb is maksaa (to cost). Because the subject of the sentence is kirjat (a plural word meaning 'the books'), the verb needs to match it by taking the 'they' form. In Finnish, the 'they' form adds -vat or -vät to the verb stem.

Does the word maksaa mean 'to cost' or 'to pay'?

It means both! You can use maksaa when talking about how much an item costs, as we see in this sentence, but you also use the exact same verb when talking about a person paying for something.