Water runs into an inverted conical tent at the rate of $20 \mathrm{f}{\mathrm{t}}^3/\mathrm{m}\mathrm{i}\mathrm{n}$ and leaks out at the rate of $5 \mathrm{f}{\mathrm{t}}^3/\mathrm{m}\mathrm{i}\mathrm{n}$. The height of the water is three times the radius of the water's surface. The rate at which the radius of the water surface is increasing when the radius is $5\mathrm{}\mathrm{f}\mathrm{t}$, is