How many gallons in an 88" x 15" x 9" trough?

Try this :

Instructions

1. Measure the rectangle length, width and height. For example, 8 inches long, 6 inches wide, 10 inches high.
   
2. Multiply the length by the height, then double the product. With this example, 8 inches multiplied by 10 inches results in 80 square inches, which multiplied by 2 equals 160 square inches.
   
3. Multiply the width by the length, then double the product. With this example, 6 inches multiplied by 8 inches equals 48 square inches, which multiplied by 2 equals 96 square inches.
   
4. Multiply the height by the width, then double the product. With this example, 10 inches multiplied by 6 inches results in 60 square inches, which multiplied by 2 equals 120 square inches.
   
5. Sum the amounts from Steps 1 through 3 to find the rectangle surface area. So adding 160, 96 and 120 square inches results in 376 square inches.