An indian tepee is a conical tent. find the number of cubic feet of air in a teepee 10 ft. in diameter and 12 ft. high.
the answer has to be like this
cu. ft

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