Learn Finnish: Onko tämä jakolasku liian vaikea? - Is this division too difficult?

In Finnish "A is B" sentences, the adjective's case depends on the subject. Because tämä jakolasku (this division problem) is a singular, countable noun, the adjective describing it must be in the basic nominative case (vaikea). You would use the partitive (vaikeaa) if the subject was uncountable (like water) or an abstract concept, for example: Onko matematiikka liian vaikeaa? (Is math too difficult?).

How is the word jakolasku formed?

It is a compound word made of jako (a division or sharing) and lasku (a calculation, count, or bill). You will see lasku at the end of all the basic math operations in Finnish, such as yhteenlasku (addition) and kertolasku (multiplication).

Could I use liikaa instead of liian in this sentence?

No, because you are modifying the adjective vaikea. Use liian when you want to say "too [adjective]" or "too [adverb]". You use liikaa when talking about an excessive amount of a noun or a verb, for example: Onko tässä liikaa työtä? (Is there too much work here?).