Learn Finnish: Paljonko tämä kirja maksaa? - How much does this book cost?

The basic word paljon means 'a lot' or 'much'. By adding the question suffix -ko, you turn it into a question word: 'how much?'. You will use paljonko a lot when asking for prices or quantities!

Since this lesson is about using the partitive case for amounts, why are tämä and kirja in their basic dictionary forms?

That is a great observation! You only use the partitive case after a number or a quantity word. Here, tämä kirja (this book) is the subject of the sentence doing the 'costing', so it stays in the basic form. If you answer the question with a number, the noun following that number will be in the partitive, like kaksi euroa (two euros).

Wait, doesn't the verb maksaa mean 'to pay'?

Yes, it does! The verb maksaa is a great two-for-one word: it means both 'to pay' and 'to cost'. When a person is the subject, it usually means 'to pay'. When an object like tämä kirja is the subject, it naturally translates to 'to cost'.