7.57 A retail grocery merchant figures that her daily gain from sales X is a normally distributed random variable with   50 and 2  10 (measurements in dollars). X could be negative if she is forced to dispose of perishable goods. Also, she figures daily overhead costs Y to have a gamma distribution with   4 and   2. If X and Y are independent, find the expected value and variance of the net daily gain.Would you expect the net gain for tomorrow to go above $70?