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 clock shows the time as 9 a. m. if the minute hand gains 7 minutes every hour, how many minutes will the clock gain by 6 p. m. ?
Options: a. 30 min, b. 35 min, c. 63 min, d. 50 min, e. 55 min
[A]: c


[Q]: Problem: in one alloy there is 10 % chromium while in another alloy it is 6 %. 15 kg of the first alloy was melted together with 35 kg of the second one to form a third alloy. find the percentage of chromium in the new alloy.
Options: a. 7.2 %, b. 9 %, c. 9.2 %, d. 8.6 %, e. 8.4 %
[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 0.20. the probability that neither a nor b occur is _________
Options: a. 0.45, b. 0.4, c. 0.55, d. 0.05, e. 0.6
[A]:
c