First you need to find the area of the base of the triangle. On the base of the triangle you use the area of a triangle formula which gives you: 1/2(20*21) which is 210. Now you have the area of the base. To find the volume (the storage space) you need to use the formula V=Area of base(height). This would then equal V = 210 (72). Finally that equals 15,120.
Your final answer is 15,120 cubic inches of space.