Learn Croatian: Zgrada ima šesnaest prozora. - The building has sixteen windows.

This sentence uses the number šesnaest (sixteen). In Croatian, numbers 5 and above require the noun that follows them to be in the genitive plural case. The basic plural for window is prozori, but the genitive plural is prozora. You can think of it as saying "sixteen of windows".

How do we make the genitive plural for a masculine noun like prozor?

For most regular masculine nouns that end in a consonant, you add -a to the end of the singular word to make the genitive plural. So, prozor (window) easily becomes prozora (of windows).

The word for six is šest. Why is sixteen spelled šesnaest without the first "t"?

Teen numbers in Croatian are formed by adding -naest to the base number, which originally meant "on ten". When šest and -naest combine, the "t" from šest is dropped to make the word smoother and easier to pronounce.

Why doesn't the verb ima change to match the plural windows?

The verb ima (has) always matches the subject of the sentence. Here, the subject is zgrada (the building), which is a singular feminine noun. Because the single building is doing the "having", we use the singular verb form.