$\"\"$

First factor the numerator and denominator.

15 = 3 · 5

21 = 3 · 7

The GCF is the product of the common prime factors in each term.

GCF = 3

$\"\"$

Divide the numerator and the denominator by GCF.

$\"\"$

$\"\"$ (Simplify) $\"\"$

Simplifest form of the fraction $\"\"$ is $\"\"$ .