Question: I would love to understand how to solve this problem: Bob wants to dig a hole 6 feet long by 4 feet wide by 3 feet deep. If it takes him 3 seconds to shovel a cubic foot of earth, how long will it take him to dig the hole?
Can you explain?
Answer: 
The hole is 6 feet long by 4 feet wide by 3 feet deep or 6 * 4 * 3 = 72 cubic feet.
Bob shovels a cubic foot of earth every 3 seconds so it will take 72 * 3 = 216 seconds to dig the hole.