Graphically,to find out how much 7.5 gallons of gasoline costs, start at the origin (where the two axes meet) and move across the x-axis (as the x-axis represents gallons of gasoline) 7.5 units. Next, move up vertically until you "hit" the graph and move left across the plane to the y-axis. You should intersect the y-axis at 6 which represents $6.00.

Algebraically, to find out how much 7.5 gallons of gasoline costs, substitute 7.5 in for x in the original equation, y = 0.80x to get, y = 0.80(7.5) = $6.00

Graphically, to find how many gallons that you could buy for $6.50, start at the origin of the graph (where the axes meet) and move up 6.5 units (representing $6.50) on the y-axis, as the y-axis represents the total amount paid for the gasoline. After you move up 6.5 units, go across the plane until you "hit" the graph. Next, move down vertically to the x axis and read the amount. It should be just a little over 8 gallonsof gasoline

Algebraically, to find how many gallons of gasoline that you could buy for $6.50, since "x" is what you are trying to find, and you know the total amount is $6.50, which is "y", substitute 6.5 in for y and solve for x in the original equation, y = 0.80x.

So, 6.5 = 0.80x. Now, dividing each side by 0.80 to solve for x, we get x = 8.125 gallons of gasoline.