You need to find a common factor that both the numerator and denominator have. 16 and 12 have common divisible factors of 2 and 4(excluding 1, because 1 is self-defined but doesn't simplify values at all).
We use the highest factor, in this case, 4.
Divide 16 by 4 and 12 by 4.
16/4 = 4
12/4 = 3
We put 4 in place of the numerator and 3 in place of the denominator.
We use the highest factor, in this case, 4.
Divide 16 by 4 and 12 by 4.
16/4 = 4
12/4 = 3
We put 4 in place of the numerator and 3 in place of the denominator.