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.

[EX Q]: Question: Pipe A can fill a tank in 16 minutes and pipe B cam empty it in 24 minutes. If both the pipes are opened together after how many minutes should pipe B be closed, so that the tank is filled in 30 minutes?

 Option A: 20

 Option B: 16

 Option C: 24

 Option D: 28

 Option E: 21
[EX A]: Option E

[EX Q]: Question: In the xy-plane, a line has slope 5 and x-intercept 3. What is the y-intercept of the line?

 Option A: -15

 Option B: -3

 Option C: 0

 Option D: 3

 Option E: 9
[EX A]: Option A

[EX Q]: Question: By selling a watch for Rs.800/-, a man loses 20% what is that watch cost price

 Option A: s. 700/-

 Option B: s. 800/-

 Option C: s. 880/-

 Option D: s. 900/-

 Option E: s. 1000/-
[EX A]:
Option E