We want to find a number, let's call it x, that satisfies the following characteristics:
We know its quotient = x/2
Then
[tex]\begin{gathered} \frac{x}{2}+9=-15 \\ \text{Solving the previous equation} \\ \frac{x}{2}=-15-9\text{ (substracting 9 both sides)} \\ \frac{x}{2}=-24\text{ (-15-9=-24)} \\ x=-24\cdot2\text{ (multiplying by 2 both sides)} \\ x=-48 \end{gathered}[/tex]