I got to the part where you have to divide (-25/2)/(5^3) and i'm stuck!
$\displaystyle \displaystyle \begin{align*} \frac{-\frac{25}{2}}{5^3} &= -\frac{25}{2} \div 5^3 \\ &= -\frac{25}{2} \times \frac{1}{5^3} \\ &= -\frac{25}{2 \cdot 5^3} \\ &= -\frac{5^2}{2 \cdot 5^3} \\ &= -\frac{1}{2 \cdot 5} \\ &= -\frac{1}{10} \end{align*}$