135 litres = 1/4 of tank
180 litres = 1/4 x 180/135 = 1/3
One-fourth of a tank holds 135 litres of water. What part of the tank is full if it contains 180 litres of water?
(1) 1/2
(2) 1/3
(3) 1/5
(4) 1/6
(5) 1/4