at 7am a sewage treatment tank contains 3000000 gallons of water. starting at 7am, x gallons per minute flow into the tank, and y gallons per minute flow out of the tank. no water enters or leaves the tank otherwise. which of the following functions f models the number of gallons of water in the sewage treatment plant at 8am?

 
You’re not providing me with the choices, so all I can say is that you want something that contains:

• 3,000,000
• +60x
• –60y

The 3,000,000 you need because that’s the starting value at 7am. The 60s you need because you’re given rates in gallons per minute and there are 60 minutes between 7am and 8am.

Hope that helps.