Question 950682
Assume you mean:

Six taps fill a empty cistern in 8 hours.
6 * 8 = 48 tap-hrs required
 How much more time will be taken if two taps go out of order.
let t = time required by the 4 remaining taps
4t = 48
t = 12 hrs required by 4 taps
But it asks how much more time.
12 - 8 = 4 more hrs