Explanation:
First find 1/4 of 72 runners. To do this divide by 4.
So
72/4=18
Now take 72 and subtract 18 to get 54
Next find 1/3 of 54 runners
54/3=18
Because it is 2/3 you need to multiply 18 by 2
So
18 x 2 = 36
So
54-36=18 runners that finished the race
If needed in fraction form
18/72
Now simplify
9/16 of the runners finished