In a recent survey of international long-distance telephone calls, many phone companies were found to be overcharging, that is, charging additional time. Suppose that the additional time being charged to an international long-distance phone call has a normal distribution with a mean of 25 seconds and a standard deviation of 8 seconds. a. Find the probability that a given international long-distance call will be overcharged by at least 40 seconds. b. By no more than 20 seconds.

c. Complete the following statement: Eighty percent of international long-distance calls are overcharged by seconds or more. I don't understand this question