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