Need help with a math Question

Hey Shereen.

The answer to the question is (E). 

Since the tank already had 7 gallons of water,  the volume expression would be given by 'x'+7, where x is the rate of flow of water in the tank. It is given that the faucet adds 1.5 gallons of water per minute. Hence the rate of flow of water is 1.5t.  This suggests that after 1 minute, the tank will have 8.5 gallons of water [ 1.5(1)+7 ] , after 2 minutes, the volume will be 10 gallons [ 1.5(2) +7] and so on.

Hope you get it.

Best of Luck. :) 

That was exactly my answer but many math teachers say that we should not count the initial 7 gal in the equation making the answer C
So I needed a confirmation from khan academy's team that it's E