Question

q(q+4)=0

Answer 1

q=0
q+4=0 => q=-4

Answer 2

I'm supposed to use the zero product property to solve that equation, isn't that an inequality?

Answer 3

Product is equal to 0 when at least one of the multipliers is equal to 0.
In this case, the multipliers are q and (q+4), so at least one of them must be equal to 0. Then you get: q=0 or (q+4)=0
The final answers are: \[q _{1}=0\]and \[q _{2}=-4\]