When Arnold makes a phone call, the amount of time that the call takes has a normal distribution with mean 6.5 minutes and standard deviation 1.76 minutes. a. 90% of Arnold's phone calls take longer than t minutes. Find the value of t. b. Find the probability that, in a random sample of 9 phone calls made by Arnold, more than 7 take a time which is within 1 standard deviation of the mean.