For this problem, we are asked to convert from one unit to another unit so we need conversion factors to be able to do this. We need to convert from gallon to cubic inches then from cubic inches to liter. We do as follows:
14 gallon ( 231 in^3 / 1 gallon ) ( 2.54 cm / 1 in )^3 ( 1 L / 103 cm^3) = 514.52 L