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: the total age of a and b is 15 years more than the total age of b and c. c is how many year younger than
Options: a. 14 years, b. 12 years, c. 56 years, d. 66 years, e. 15 years
e

Problem: for each of her sales, a saleswoman receives a commission equal to 20 percent of the first $ 500 of the total amount of the sale, plus 35 percent of the total amount in excess of $ 500. if the total amount of one of her sales was $ 800, the saleswoman ' s commission was approximately what percent of the total amount of the sale ?
Options: a. 22 %, b. 24 %, c. 25 %, d. 26 %, e. 28 %
d

Problem: find the simple interest on $ 1000 for 3 years at 10 % per annum ?
Options: a. $ 250, b. $ 300, c. $ 500, d. $ 600, e. $ 1000
b