Explanation:

let tap take t time
due to leakage, it takes an extra 30 hours
total time t+30 hours
tank filled in t+30 when leakage work
the capacity of leakage is 2t
(t+30)(1/t - 1/2t)=1
(t+30)(1/2t)=1
t+30=2t
t=30 hours
leakage capacity 2t hours=72 hours