What I understand from the picture given, she had 2 ribbons with the length of 1/4.
These would be the two shortest ones.
So: 1/4 + 1/4 = 2/4
= 1/2
I hope this helps and I know that it is different to what HimyBrainy put but it is what I understood! :/
This is not possible, because if you had 11 coins, then not even 11 dimes will cover it, because 11*10 is 110, or $1.10
Parameterize the lateral face

of the cylinder by

where

and

, and parameterize the disks

as


where

and

.
The integral along the surface of the cylinder (with outward/positive orientation) is then



