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.

[EX Q]: Problem: of 30 applicants for a job, 9 had at least 4 years ' experience, 18 had degrees, and 3 had less than 4 years ' experience and did not have a degree. how many of the applicants had at least 4 years ' experience and a degree ?
Options: a. 14, b. 10, c. 9, d. 7, e. 5
[EX A]: b

[EX Q]: Problem: when positive integer n is divided by 7, the remainder is 1. when n is divided by 11, the remainder is 5. what is the smallest positive integer k such that k + n is a multiple of 77 ?
Options: a. 2, b. 4, c. 6, d. 8, e. 10
[EX A]: c

[EX Q]: Problem: a hollow iron pipe is 21 cm long and its external diameter is 8 cm. if the thickness of the pipe is 1 cm and iron weighs 8 g / cm 3, then the weight of the pipe is :
Options: a. 3.6 kg, b. 3.696 kg, c. 36 kg, d. 36.9 kg, e. none
[EX A]:
b