I don’t understand how to solve this

so mean = average so your going to take the three lifespan numbers  so if there is 20 10 month life spawns 15 10.5 month lifespans and 25 11 month lifespans you will lay your numbers out like this --10, 10, 10, 10, 10 , 10 , 10 , 10, 10 , 10 , 10 , 10, 10 , 10 , 10 , 10, 10 , 10 , 10 , 10, 10.5, 10.5, 10.5, 10.5,  10.5, 10.5, 10.5, 10.5, 10.5, 10.5, 10.5, 10.5, 10.5, 10.5, 10.5, 11, 11, 11, 11, 11, 11, 11, 11, 11,11, 11, 11, 11, 11,11, 11, 11, 11, 11,11, 11, 11, 11, 11, 11 now add all those up and divide by the amout in this case that would be 60 so when you add all those up the sum is 632.5 now take the sum and divide by 60 632.5/60=10.5416666667 so 10.5416666667   is your mean aka average      ples give brainliest