Hi there!
In order to find the shaded area, we'll need to find the area of the larger circle and subtract the area of the smaller circle from it.
WORK:
A = pi x 36 (larger)
A = 36pi
A = pi x 16 (smaller)
A = 16pi
36pi - 16pi = 20pi or 62.8cm^2
When a radius is doubled, the entire area is quadrupled. This is because the radius is squared.
Hope this helps!! :)
If there's anything else that I can help you with, please let me know!