Area of the rectangle 1 = base x height
 = 45 x 24 
 = 1080
Area of the circle = pi r^2
 = (3.1416) (5)^2
 = 78.54
Final area of the rectangle = 1080 - 78.54
 a) = 1001.46 cm^2
b) 
 1080 -------------------- 100
 78.54 ------------------ x
 x = (78.54 x 100)/1080
 b) x = 7.27 %