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: of 60 children, 30 are happy, 10 are sad, and 20 are neither happy nor sad. there are 19 boys and 41 girls. if there are 6 happy boys and 4 sad girls, how many boys are neither happy nor sad ?
Options: a. 2, b. 7, c. 6, d. 8, e. 10
b