Question 99471
the surface area of the cylinder is the lateral area (2*pi*r*15) plus the area of the 2 ends (2*pi*r^2)


30*pi*r+2*pi*r^2=2*pi*(r+6)^2 ... dividing by 2*pi gives 15r+r^2=(r+6)^2


15r+r^2=r^2+12r+36 ... 15r=12r+36 ... 3r=36 ... r=12