Two random variables are such that A has a mean of 80 and standard deviation of 12, while B has a mean of 140 and a standard deviation of 18. Both are roughly normal, and they ARE independent. Show your work for the following, answer the questions below, and submit your work at the end. a) Define D to be the difference: D= B - A. Find the mean of D. b) Find the standard deviation of D. Finally, c) If we randomly chose an A and B value, then what is the probability that D is less than 30?