arithmetic - two pipes a and b together can fill a cistern in 4 hours had they been opened separately then b would have taken 6 hours more than a to fill the cistern how much time will be taken by a to fill the cistern separately - skillgun

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