Compare the unit rates at which both tanks are leaking.
Tank A is losing water at a rate of
(1/16 gal) / (1/12 min) = 12/16 gal/min = 0.75 gal/min
Tank B is losing water at a rate of
(3/80 gal) / (1/30 min) = 90/80 gal/min = 1.125 gal/min
So Tank B is losing water faster.