The relationship between the number of gallons of water in a tank and number of hours is proportional. One point on the line modeling the relationship is (2,7200). Find the slope of the line, and draw a graph. Use the graph to find how long it will take to fill the tank if it holds 72,000 gallons. The slope of the line is __

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.

what i would say the best answer is a. 40.5