Given a math problem with context and a question and 5 answer choices, the task is to provide the correct answer choice based on the problem. You must choose one of the given answer choices by letter: a, b, c, d, or e; anything else is invalid.

[EX Q]: Problem: if jack walked 8 miles in 1 hour and 15 minutes, what was his rate of walking in miles per hour ?
Options: a. 4, b. 4.5, c. 6, d. 6.4, e. 15
[EX A]: d

[EX Q]: Problem: a 11 % stock yields 8 %. the market value of the stock is :
Options: a. rs. 72, b. rs. 137.50, c. rs. 112.50, d. rs. 116.50, e. none of these
[EX A]: b

[EX Q]: Problem: if y > 0, ( 4 y ) / 20 + ( 3 y ) / 10 is what percent of y ?
Options: a. 40 %, b. 50 %, c. 60 %, d. 70 %, e. 80 %
[EX A]:
b