A water tower that is $90 \mathrm{ft}$ high provides water to a residential subdivision. The water main from the tower to the subdivision is $6 \mathrm{in}$. sch 40 steel, 3 miles long. If each house uses a maximum of $50 \mathrm{gal} / \mathrm{h}$ (at peak demand) and the pressure in the water main is not to be less than 30 psig at any point, how many homes can be served by the water main?