let "r" be the radius of cylinder and "h" be the height.
Formula for surface area is:
S= 2r^2pi + 2rpih
where 24^2pi is surface of two bases of cylinder and 2rpih is surface of mantle.
One of the tasks conditions is that h = 2r.
S = 2r^2pi + 2r2rpi
second and last condition is r=(2x+3). Now we express this as well.
S = 2(2x + 3)^2 pi + 4(2x+3)^2pi=6pi(2x+3)^2
S = 6pi(4x^2+12x + 9)
S = 24pix^2 + 72pix + 54pi
