Remark
You need 2 facts to solve this
1. The area of a hexagon is
A = 3*(sqrt(3) ) * a^2/2
Just to make this clear, I'll put it in Latex
2. The second fact you need to know is that the radius = the length of the side a.
Givens
r = 20 in
a = r where a is the length of the side of a hexagon.
Formula Substitute and solve.
A = 3*(sqrt(3) * a^2 ) / 2
A = 3*(sqrt(3) * 20^2) / 2
A = 3*sqrt(3) * 400 / 2
A = 3*sqrt(3) * 200
A = 3*1.7321 * 200
A = 1039 square inches.