7. 3.14(12^2 - 10^2)=3.14(144-100) = 3.14(44)=138.16
8. A = piR^2 = 50.24. R^2 = 50.24/3.14 = 16. R = 4cm
9a) Perimeter of square is 4*18 = 72. Perimeter of circle is 2*pi*r. r=9in
perimeter of circle is then 2*3.14.9 = 56.52. Difference is 72-56.52 = 15.48
9b) Area of square is 18^2 = 324.
Area of circle is 3.14(9^2) = 254.34. Difference is the unshaded part
324-254.34 = 69.66in^2