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.

Q: Problem: a student travels from his house to school at 12 km / hr and reaches school 2 hours late. the next day he travels 20 km / hr and reaches school 1 hour early. what is the distance between his house and the school ?
Options: a. 90, b. 100, c. 110, d. 120, e. 130

A: a
****
Q: Problem: the probability of two events a and b are 0.25 and 0.40 respectively. the probability that both a and b occur is 0.15. the probability that neither a nor b occur is _________
Options: a. 0.45, b. 0.4, c. 0.5, d. 0.05, e. 0.6

A: c
****
Q: Problem: in a certain supermarket, a triangular display of cans is arranged in 9 rows, numbered 1 through 9 from top to bottom. each successively numbered row contains 3 more cans than the row immediately above it. if there are fewer than 120 cans in the entire display, how many cans are in the seventh row ?
Options: a. 13, b. 15, c. 17, d. 19, e. 21

A:
d
****