7.79. Successive weekly sales, in units of one thousand dollars, have a bivariate normal distribution with common mean 40. common standard deviation 6, and correlation .6. (a) Find the probability that the total of the next 2 weeks' sales exceeds 90. (b) If the correlation were .2 rather than . 6, do you think that this would increase or decrease the answer to (a)? Explain your reasoning. (c) Repeat (a) when the correlation is .2