Hey there!
It looks like we're factoring.
I always like to think of factoring as the opposite of the distributive property, and you'll see why.
First, we have to factor out a common factor from 21p and 35q, which we'll use as 7.
7 times 3p = 21p and 7 times 5q = 35q
Using our distributive property which is defined as:
a(b+c) = ab+ac we have:
7(3p + 5q)
Multiply it out and you'll get 21p and 35q.
Hope this helps!