To find the mean, you need to add up all the numbers and then divide by the total number of numbers.
90.75 + 99.17 + 71.80 + 100.00 + 97.33 + 79.58 + 92.58 + 87.09 + 81.59 + 91.86 + 94.18 = 985.93
There are 11 numbers, so we divide the sum by 11:
985.93 ÷ 11 = 89.63
Rounded to the nearest hundredth, the mean is 89.63.