Answer:
Step-by-step explanation:
I am assuming the tank starts empty. It means that in 1 hour the tank has half that water, or 3600 gallons. And the good thing of lines passing through 0.0 is that the value at 1 IS the slope we need. ie 3600.
At this point it's easy to find that if in 2 hours it filled 1/10th of the tank, in 20 hours the tank will be full.
Graph done with paint, obviously not to scale.
