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: cost is expressed by the formula tb ^ 4. if b is doubled, the new cost w is what percent of the original cost ?
Options: a. w = 200, b. w = 600, c. w = 800, d. w = 1600, e. w = 50
d

Problem: if an investor puts $ 700 in a savings account that earns 10 percent annual interest compounded semiannually, how much money will be in the account after one year ?
Options: a. $ 769.75, b. $ 771.75, c. $ 773.75, d. $ 775.75, e. $ 777.75
b

Problem: find the ones digit of 73 ^ 300
Options: a. 3, b. 5, c. 6, d. 7, e. 10

e