How do you solve for the x and y variables

Create a real-life situation and create a system and show how it might be modeled algebraically with a system of equations (or inequalities) show all work include a few sentences explaining the situation, your variables of choice and what each represents, and how you would set it up and solve it algebraically. !

The graph represents the gallons of water in a water tank with respect to the number of hours since it was completely filled

Me find the value of x each figure.