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: in one hour, a boat goes 19 km / hr along the stream and 9 km / hr against the stream. the speed of the boat in still water ( in km / hr ) is :
Options: a. 12 kmph, b. 13 kmph, c. 14 kmph, d. 15 kmph, e. 16 kmph

A: c
****
Q: Problem: mrs. evans gave a test to her freshmen economics class, which has 29 students enrolled and 19 of them answered question 1 correctly. if 24 answered question 2 correctly and 5 did not take the test then how many answered both questions correctly ?
Options: a. 3, b. 9, c. 11, d. 17, e. 19

A: e
****
Q: Problem: the average age of 40 students in a class is 10 years. if teacher ' s age is also included then average increases 1 year then find the teacher ' s age ?
Options: a. 59, b. 55, c. 61, d. 51, e. 36

A:
d
****