Question: John has two jobs. For daytime work at a jewelry store he is paid $200 per month, plus a commission. His monthly commission is normally distributed with mean $600 and standard deviation $40. At night he works as a waiter, for which his monthly income is normally distributed with mean $100 and standard deviation $30. John's income levels from these two sources are independent of each other. For a given month,

A. What is the probability that John's commission from the jewelry store is less than $640?

B. The probability is 0.9 that John's income as a waiter is less than how much?