The correct option is D 5 min.
Let the capacity of the tank be 40 (LCM of 8, 10 & 40).
A fills = 408 = 5 units / minute.
B fills = 4010 = 4 units / minute.
C empties = 4040 = -1 unit / minute.
(A + B + C)s per minute work = 5 + 4 - 1 = 8 units/min.
Time taken by (A + B + C) together to fill the tank = 408 = 5 minutes.