Range of the graph is the ALLOWED y-values. The y-axis is number of gallons left in tank. So, <u><em>it cannot be NEGATIVE number of gallons, so 0 is the lower limit of the range.</em></u>
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As we can see from the axis of the graph, we see where the line cuts the y-axis, that is the upper limit of number of gallons he starts off with. The y-intercept (y-axis cutting point) is 12.