I just took this quiz and got 100% and your answer is 2cm. I didn't get it at first but i get it now.
3.14*5*5*471=36,973.5
3.14*5*5*314=24,649
36,973.5-24,649=12,324.5
471/314=1.5
1.5 is about 2 rounding
P.S
(This is just how i figured it out it might not work every time.)