A rotary drum filter has a diameter of $6 \mathrm{ft}$ and a length of $8 \mathrm{ft}$ and rotates at a rate of $30 \mathrm{~s} / \mathrm{cycle}$. The filter operates at a vacuum of $500 \mathrm{~mm} \mathrm{Hg}$, with $30 %$ of its surface submerged. The slurry to be filtered is tested in the lab using $0.5 \mathrm{ft}^{2}$ of the drum filter medium in a filter funnel operating at $600 \mathrm{~mm} \mathrm{Hg}$ vacuum. After $5 \mathrm{~min}$ of operation, $250 \mathrm{~cm}^{3}$ of the filtrate was collected through the funnel, and after $10 \mathrm{~min}$, a total of $400 \mathrm{~cm}^{3}$ is collected. What would be the net (average) filtration rate of this slurry in the rotary drum filter, in gpm?