A small leaf filter is run at constant rate. It is found that the initial pressure is 5 psig and the pressure after 20 minutes of operation during which 30 gallons of filtrate is collected is 50 psig. If this filter is used with the same slurry in a constant pressure filtration at 50 pig, the filtrate collected in 20 minutes is

The supposed answer is 41.5 gal. Please show detailed solution and explain. Thank you.