Answer:
C. Logan
Step-by-step explanation:
you divide the amount of problems by how many minutes it took each person. for example if you divide the amount of problems Logan did by how many minutes it took him. (84÷3) it equals 28.
30=2*3*5, so it's 30
15=3*5, so it's not 15
20=2*2*5, so it's not 20
57=19*3, so it's not 57
63
7, 14, 21, 28, 35, 42, 49, 56, 63, 70.
9, 18, 27, 36, 45, 54, 63, 72, 81, 90.
A:63