I need help with a surface area question.

Jake is going to put plastic lining inside a rectangular pond. The pond has a width of 6ft, length of 9ft, and a depth of 3ft. Jake incorrectly calculates the surface area of the inside of the pond. What is the correct answer?

He got: 198 ft squared.
He used the formula correctly, but I believe that you have to do the inside of the pool, the correct answer should be 144 ft squared.

Question

I need help with a surface area question. 

Jake is going to put plastic lining inside a rectangular pond. The pond has a width of 6ft, length of 9ft, and a depth of 3ft. Jake incorrectly calculates the surface area of the inside of the pond. What is the correct answer?

He got: 198 ft squared. 
He used the formula correctly, but I believe that you have to do the inside of the pool, the correct answer should be 144 ft squared.

anonymous · Answer

I just don't remember how to go about this. An explanation would be appreciated. :)