You will be given a definition of a task first, then some input of the task.
You are given a math word problem and you are supposed to make use of mathematical concepts like probability, combinatorics, linear equations, sequences/series, or simple operators like addition, subtraction, division, or multiplication to answer the given question. Choose the best option from the 5 given options and report that option.

Question: Pumping alone at their respective constant rates, one inlet pipe fills an empty tank to 1/4 of capacity in 9 hours and a second inlet pipe fills the same empty tank to 2/3 of capacity in 6 hours. How many hours will it take both pipes, pumping simultaneously at their respective constant rates, to fill the empty tank to capacity?

Option A: 3.25

Option B: 3.6

Option C: 4.2

Option D: 4.4

Option E: 7.2
Output:
Option E