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: if the simple interest on a certain amount in at 4 % rate 5 years amounted to rs. 2240 less than the principal. what was the principal ?
Options: a. 1500, b. 2500, c. 2507, d. 2800, e. 11500
d

Problem: the grade point average of one third of the classroom is 15; the grade point average of the rest is 18. what is the grade point average of the whole class ?
Options: a. 17, b. 19, c. 21, d. 23, e. 25

a