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: 8 persons can build a wall 140m long in 42 days. In how many days can 30 persons complete a similar wall 100 m long?

 Option A: 12

 Option B: 10

 Option C: 8

 Option D: 6

 Option E: 5
[EX A]: Option C

[EX Q]: Question: The difference of two numbers is 1565. On dividing the larger number by the smaller, we get 6 as quotient and the 15 as remainder. What is the smaller number ?

 Option A: A

 Option B: B

 Option C: C

 Option D: D

 Option E: E
[EX A]: Option E

[EX Q]: Question: David invested a certain sum of money in a bank that paid simple interest. The amount grew to $300 at the end of 2 years. He waited for another 3 years and got a final amount of $390. What was the principal amount that he invested at the beginning?

 Option A: $340

 Option B: $300

 Option C: $280

 Option D: $260

 Option E: $240
[EX A]:
Option E