You roll a​ die, winning nothing if the number of spots is odd​, ​$5 for a 2 or a 4​, and ​$20 for a 6. ​a) Find the expected value and standard deviation of your prospective winnings. ​b) You play five times. Find the mean and standard deviation of your total winnings. ​c) You play 50 times. What is the probability that you win at least ​$270​?