Hello!
let me guide you through this step by step:
if you add the total number of hamburgers eaten you will get 120
the adults ate 81 out of the 120 total
to find the percentage, divide 81 by 120, then multiply by 100 to find the percentage
81/120=0.675
0.675*100=67.5
your final answer is 67.5
I hope this helps, and have a nice day.