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: if a mixture is 1 ⁄ 7 alcohol by volume and 2 ⁄ 7 water by volume, what is the ratio of the volume of alcohol to the volume of water in this mixture ?
Options: a. 4 / 2, b. 3 / 2, c. 1 / 2, d. 5 / 2, e. 7 / 2

A: c
****
Q: Problem: if julie rows 32 km upstream and 72 km down steam taking 4 hours each, then the speed of the stream
Options: a. 1.5 kmph, b. 0.5 kmph, c. 0.4 kmph, d. 1.6 kmph, e. 2.5 kmph

A: b
****
Q: Problem: if ( a + b. = 4, ( b + c. = 8 and ( c + d. = 3, what is the value of ( a + d. ?
Options: a. 16., b. 8., c. 7., d. 2., e. - 1.

A:
e
****