3, 5, and 7.
7919
Two.
Nope - it can be divided by 3.
It doesn't have two factors.
No, it is an even number and therefore can be at least divided by 2.
11/12 cannot be simplified - because 11 is a primenumber.
It's already in its simplest form - 67 is a primenumber.
18/29 cannot be simplified - because 29 is a primenumber !
I could bore you with a long mathematical explanation (ask if you want one), but to simplify things, 2 is a prime number.
23 doesnot belong because it is a primenumber. Its factors are 1 and itself only.34 and 45 are compositenumbers. Their factors aside from 1 and themselves are:34 = 2, 1745 = 3, 5, 9, 15,
It's already in its simplest form - since 43 is a primenumber.