Theme and Variations

If x varies directly with $\sqrt{y}$ , then x = $\sqrt{y}$ $\times$ c, where c is an undetermined constant. If x = 8 and y =8, then c = $\frac{x}{\sqrt{y}}$ = $\frac{8}{\sqrt{8}}$ = $\sqrt{8}$ . When y = 72, x = $\sqrt{72}$ $\times$ $\sqrt{8}$ = 3 $\sqrt{8}$ $\times$ $\sqrt{8}$ = 3 $\times$ 8 = $\boxed{24}$