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.

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
d

Problem: the difference between the compound interest compounded annually and simple interest for 2 years at 20 % per annum is rs. 216. find the principal ?
Options: a. 2277, b. 2667, c. 5400, d. 2766, e. 1811
c

Problem: a certain car uses 12 gallons of gasoline in traveling 120 miles. in order for the car to travel the same distance using 10 gallons of gasoline, by how many miles per gallon must the car ’ s gas mileage be increased ?
Options: a. 2, b. 4, c. 6, d. 8, e. 10

a