Amount of paper is going to be measured in area, so we want the surface area of the cone. Since it is a cub it doesn't have a base, so we don't need to count it.
Area of the cone without the base, or what is called the lateral area is pi*r*s where r is the radius and s is the slant height. and of course radius is d/2 where d is the diameter. so let's plug it in. We know diameter is 6 and slant height is 7.5
SA = pi * r * s
SA = pi * d/2 * s
SA = pi * 6/2 * 7.5
SA = 22.5 cm^2
So you will need 22.5 square centimeters of paper.
