Discussion

Explanation:

Half of the tank is filled by tap X in 30 hours. Hence, the tank is fully filled by tap X in 60 hours.

The tank is initially half full and it would take 30 hours to fill the tank.

Part of the tank filled in 6 hours = $\frac{6}{10}$ = $\frac{1}{10}$ ^th 

Now, according to the question, amount of water in the tank = $\frac{1}{2}$ + $\frac{1}{10}$ = $\frac{6}{10}$ ^th 

After this, half of water has been used up during the supply cut.

∴ The remaining water = $\frac{3}{10}$ ^th  
The part of tank still empty = 1 – $\frac{3}{10}$ = $\frac{7}{10}$ ^th  

Time taken to fill $\frac{7}{10}$ ^th  of the tank = $\frac{7}{10}$ × 60 = 42 hours

Hence, option (c).

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