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: Find the average of all prime numbers between 4 and 15.

 Option A: 30

 Option B: 4

 Option C: 9

 Option D: 8

 Option E: None
[EX A]: Option C

[EX Q]: Question: Find the fourth proportion to 2,4,6

 Option A: 18

 Option B: 12

 Option C: 9

 Option D: 6

 Option E: 8
[EX A]: Option B

[EX Q]: Question: KODAK bank offers an interest of 5% per annum compounded annually on all its deposits. If $10,000 is deposited, what will be the ratio of the interest earned in the 4th year to the interest earned in the 5th year?

 Option A: 1:5

 Option B: 625:3125

 Option C: 100:105

 Option D: 100^4:105^4

 Option E: 725:3225
[EX A]:
Option C