Surface Area of a cone is
pi * r * s + pi * r^2
s is the side length, since you have 10 ft diameter, you know radius is 5. And since height is 12. With this, you have a 5-12-13 triangle, and s=13.
so
pi * 5 * 14 + pi * 5^2 = 95 pi or 298.3
divide 298.3 by 15 and you get 19.88, you round up, so 20 is the answer
