In a stem and leaf plot, the numbers on the left side of the line represent the tens digit in a number and the right side represent the ones digit. Therefore you have the numbers 15, 18, 46, 50, 50, 50, 50, and 57. The question asks you to find the mean, or the average of the numbers. So all you have to do is add up the numbers and divide it by 8 and that'll leave you with 42.
