First of all, the two figures are equivalent. Find the area of the rectangle and you'll get the area of the circle
A(r) = A(c) = W*L = 2*11 = 22 ft²
A(c) = πr²
π = 22/7
So
22/7*r² = 22
Multiply both sides for 7/22 to get rid of the fraction.
7/22 * 22/7 * r² = 22 * 7/22
r² = 7
r = √7
