An aqueous slurry containing $1.5 \mathrm{lb}_{\mathrm{m}}$ of solid per gallon of liquid is pumped through a filter cloth by a centrifugal pump. If the pump provides a constant pressure drop of $150 \mathrm{psig}$, how long will it take for the filter cake to build up to a thickness of 2 in.? The density of the filter cake is $30 \mathrm{lb}_{\mathrm{m}} / \mathrm{ft}^{3}$ and its permeability is 0.01 darcies.