To find the mean you must add all the numbers together then divide the sum by the total amount of numbers in the data set
71 + 92 + 94 + 93 + 98 + 85 + 66 + 70 + 68 + 93 + 87 + 71 + 85 + 52 + 61 + 62 + 85 + 69 + 95 + 79 = 1576
There are at total of 20 numbers in this data set so you must divide 1576 by 20
1576 / 20 = 78.8
Hope this helped!
~Just a girl in love with Shawn Mendes