The shaded region is the big rectangle minus the smaller, inner one.
The area of any rectangle is its base multiplied by its height.
The area of the big rectangle is (5x+2)(3x-1), and the area of the small one is x(x+7). So the area of the shaded region is (5x+2)(3x-1)-x(x+7), computing the algebra:
Well we know that the volume of a cylinder equals (area of base) (height) 225pi=a*9 divide both sides by 9 25pi=a a=pir^2 25pi=pir^2 cancel out pi 25=r^2 5=r so the length of the radius is 5
