Correct Answer: Option C
Let the cistern be filled by pipe A alone in x hours.
Then, pipe B will fill it in (x + 6) hours.
So, 1/x + 1/(x + 6) = ¼
=> (x + 6 + x)/ x(x + 6) 4 = 1/4
=> x2 - 2x - 24 = 0
=> (x -6)(x + 4) = 0
=> x = 6. [neglecting the negative value of x]
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