Answer:
it's either a or b, but I would go with A
2 Hours
this is because one pipe takes 4 hours, and if both pipes take 2 hours, that is cutting the time in half, meaning both pipes pour the same amount and take the same time.
hope this is helpful!
What you are asking is

we need to make the fractions improper now,

now we need common denominators:

we get

OR
The answer is D because the median is the midpoint of the distributed numbers