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: the average height of 30 girls out of a class of 40 is 160 cm. and that of the remaining girls is 156 cm. the average height of the whole class is :
Options: a. 158 cms, b. 158.5 cms, c. 159 cms, d. 159.5 cms, e. none
c