The number is prime if it is not divisible by anything other than itself or 1.
35 / 7 = 5, so 35 is not it.
69 / 3 = 23, so that's not it either.
89 cannot be divided evenly by anything other than one or itself. This is your answer!
(Side note: 90 can be divided by 10, and 10 can be divided by 2)
hope it helped
