Given the task definition and input, reply with output. 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.

Problem: solution a is 30 % salt and solution b is 80 % salt. if you have 30 ounces of solution a and 60 ounces of solution b, in what ratio could you mix solution a with solution b to produce 50 ounces of a 50 % salt solution ?
Options: a. 6: 4, b. 6: 14, c. 4: 4, d. 4: 6, e. 3: 2
e