Question

solve using the zero principle of zero products
r(r+4)=0

Answer 1

r=0
r=-4

Answer 2

In order for r(r + 4) to equal 0, either r or (r+4) must be zero. This is because any number times 0 equals 0.
So, we make two problems.
First:
r = 0
Second:
(r + 4) = 0
r = -4
Your two solutions are r = 0, -4