I am overthinking this but $(-4)}^{(-\frac{5}{2})$ is not a valid equation, am I correct? Working through the problem gives me $\frac{1}{-{4}^{\frac{5}{2}}}$ which then works out to $\frac{1}{\sqrt{-{4}^{5}}}$ which leaves a negative number in the square root, which is not valid.