The line equation in slope-intercept form is ,

where m is the slope and b is the y-intercept.

Write the two functions as co-ordinates

as

as

First find the slope

m =

    =                    (Substitute and )

    =                      (Apply additive identity property: a + 0 = a)

     = 3                        (Divide: )­­

The line crosses the y-axis at (0, 9). So the y-intercept is 9.

Substitute and in slope-intercept form line equation.

                  (Simplify)

The function is .