The area of the larger rectangle is \begin{align*}8(16)=128 \ \mathrm{units}^2\end{align*} and the area of the smaller rectangle is \begin{align*}5(10)=50 \ \mathrm{units}^2.\end{align*} If we compare the areas in a ratio, it is \begin{align*}50:128 \ = \ 25:64 \ = \ 5^2:8^2.\end{align*}
