Question 37022
If you look at the equation (q+4)(3q-15)=0 you may notice that the solutions of this equation is given by the two numbers for which one of the factors it is equal zero. Those numbers are -4 and 5, therefore q=-4 or q=5.

Explanation:

When you multiply to numbers and get as a result 0 one of the factors must be cero.
If a*b=0, then a, b or both a and b are equal to zero.
We will apply this to solve the problem.

If (q+4)(3q-15)=0, then (q+4)=0 or (3q-15)=0, then we only have to solve this two linear equations to find the solutions.

q+4=0, as a result q=-4, the first solution.
3q-15=0, as a result q=5. the second solution.

I hope that you could understand everything, if you have any doubt please tell me.