The length of time for long-distance phone calls has been found to be normally distributed, with a mean of 24.7 minutes and a standard deviation of...

The length of time for long-distance phone calls has been found to be normally distributed, with a mean of 24.7 minutes and a standard deviation of 4.7 minutes. In a randomly selected sample of 50 calls, what is the sample average call time below which 10% of sample average call times will be shorter? (2 decimal places)