Question

factor.
28u + 21

Explanation:

Step1: Find GCD of 28 and 21

The greatest common divisor of 28 and 21 is 7, since $28=7\times4$ and $21=7\times3$.

Step2: Factor out the GCD

Rewrite each term as a product of 7 and another factor, then factor out 7:
$28u + 21 = 7\times4u + 7\times3 = 7(4u + 3)$

Answer:

$7(4u + 3)$