t or time is the unknown here to be solved.
The hours Ivan rent the boat multiplied with $8 with $9 discount needs to be less than $31. Hence,
8t - 9 < 31
8t < 31 + 9
8t < 40
t < 5
The hours Ivan can rent the boat has to be less than 5. This is because he wants to spend LESS than 31, 31 sharp is not okay.