243 liters represents 7/10 - 1/4 of the water.
v=243 / (7/10 - 1/4) = 243 / (14/20-5/20) = 243(20)/9 = 540 liters.
Answer: 540 liters
Check:
(7/10)(540) = 7(54) = 378
(1/4)540 = 135
difference = 378 - 135 = 243 good
