A large building has a roof with dimensions $50 \mathrm{ft} \times 200 \mathrm{ft}$, which drains into a gutter system. The gutter contains three drawn aluminum downspouts that have a square cross section, 3 in. on a side. The length of the downspouts from the roof to the ground is $20 \mathrm{ft}$. What is the heaviest rainfall (in./h) that the downspouts can handle before the gutter will overflow?