To determine the number of gallons of gasoline Trisha can purchase with $30, we refer to point X on the graph, which is located at (9.375, 30). This indicates that at a cost of $30, she can purchase approximately 9.375 gallons of gasoline.
Rounding 9.375 to the nearest whole number gives us 9 gallons.
So, the answer is:
9 gallons