So first count all of the numbers that are left. There are a total of 19 numbers. Then count the numbers that are divisible by 3 (3, 21, 36, 42, 45, 51, 54, 86, 90). These are 9 total numbers. So you would make a fraction 9/19. I think you are missing a number because I don’t see an option for 9/19. Check if you are missing a number. You should be missing exactly number, so go check and if you are, choose 9/20.