four outlet pipes

The four outlet pipes are at the following positions:
4th one at the bottom most
3rd one at 1/4th height from bottom
2nd one at 1/2 the height from bottom
1st one at 3/4th height from bottom

The inlet pipe fills the tank to full in an hour's time.
Each outlet pipe can empty in 4 hr => all four at a time can empty in 1 hr
If 3 pipes are working at a time, the can empty in 4/3 hr
If 2 pipes are working at a time, the can empty in 4/2 hr
After vacating the top 1/4th portion, the effect of top most pipe is not considered as the water level reaches it's height.Similarly, after vacating 1/2 of the portion, the effect of top-second pipe is also not considered as such the effect of top-thrid pipe after vacating 3/4th portion.
The top-most pipe is at a distance of 1/4th height from top => first 1/4th portion is emptied by all the four pipes in 1/4 * 1 = 1/4 hr
The top-second pipe is at a distance of 1/4th height from the top-first pipe => second 1/4th portion is emptied by the remaining three pipes in 1/4 * 4/3 = 1/3 hr
The top-3rd pipe is at a distance of 1/4th height from the top-2nd pipe => third 1/4th portion can be emptied by the remaining two pipes in 1/4 * 4/2 = 1/2 hr. But After emptying the first two fourths, the time left out
= 1-(1/4 + 1/3) = 5/12 hr , which is less than 1/2 hr.
The remaining two pipes can empty (5/12)/(4/2) = 5/24th portion.
Conclusion:
After 1hr time, the portion of tank with water = 1-(1/4 + 1/4 + 5/24) = 7/24th
=> The portion to be filled by the inlet pipe = 1 - 7/24 = 17/24
The inlet pipe can fill the tank to full in 1 hr => it can fill 17/24th of tank in 17/24 hr
= 17/24 * 60 min = 42.5 min
Answer "B"