First, we'll find the area of the base. (To find the volume of any prism, find the area of the base, then multiply by the length/height.) It consists of a rectangle and a semicircle put together. To find the area of the semicircle, we'll just use the formula for the area of a circle, then divide by two. Area of a circle = radius² × 3.14. If the diameter of this circle is 8, then halve that to find the radius, which is 4. 4² = 16. 16 × 3.14 = 50.24. Now, 50.24/2 = 25.12. 25.12 is the area of the semicircle. Then, find the area of the rectangle. Formula for that is base × height. 6 × 8 = 48. Now add the two areas. 25.12 + 48 = 73.12.
Simply multiply that area by the length to find the volume. 73.12 × 15 = 1096.8.
The volume of the mailbox is 1,096.8 in³. (Don't forget to label!)
Hope that helped!