Treat the data as ordered pairs. From the table, write the year as x - coordinate and the gallons as y - coordinate.

Plot the ordered pairs as points in a coordinate plane.

The scatter plot shows a positive correlation between x and y. This means that as the x - values increased, the y - value tended to increase, so you can fit a line to the data.

Draw a line that appears to fit the points in the scatter plot closely.

Write an equation using any two points on the line.

Substitute the values of in the slope formula .

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To write the line equation, we can use either of the two given points.

Consider the point .

Substitute in point-slope form equation or .

Apply distributive property: .

Add 29 to each side.

The line equation is .

Substitute the value of in the above equation.

Subtract 11.5 from each side.

Divide each side by 1.25.

Cancel common terms.

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The missing value is 7, the equation is and its graph is