How is this done

2) Emelyn and Arlene attend the same high school and take the same math class. The time E that it takes Emelyn to do her math homework follows a Normal distribution with mean 25 minutes and standard deviation 5 minutes. Arlene's math homework time A follows a Normal distribution with mean 50 minutes and standard deviation 10 minutes. Assume that E and A are independent random variables. a) Randomly select one math assignment of Emelyn's and one math assignment of Arlene's. Let the random variable D be the difference in the amount of time each student spent on their assignments: D : A E. Find the mean and the standard deviation of D. Show your work. b) Find the probability that Emelyn spent longer on her assignment than Arlene did on hers. Show your work