To find the mean/data of a set of numbers, add all of the numbers together then divide by the number of numbers there are.
85+93+80+89+92+93+94+91+79 = 796
796/9 = 88.4444444 which can be rounded down to 88.4
The answer is 88.4.
Hopefully this helps! If you have any more questions or don't understand, feel free to DM me, and I'll get back to you ASAP! :)