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: 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
Option E

Question: A board of length L feet is cut into two pieces such that the length of piece A is 4 feet less than three times the length of piece B. Which of the following is the length, in feet, of piece A?

Option A: (L+4

Option B: (L-4

Option C: (3L-4

Option D: (3L-1

Option E: (3L+4
Option C

Question: In what ratio should a variety of rice costing Rs. 6 per kg be mixed with another variety of rice costing Rs. 8.75 per kg to obtain a mixture costing Rs. 7.50 per kg?

Option A: 1/68

Option B: 62/89

Option C: 12/68

Option D: 11/84

Option E: 5/6
Option E