A line equation can be written in slope-intercept form. The slope-intercept form is
Where m represents the slope and b the y-intercept.
We can substitute our points on this form to get a system of equations to find the slope and y-intercept of our desired line. Using the points (- 42.75, 5.7) and (2.75, 4.1), we have
If we subtract the second equation from the first equation, we get a new equation only for the slope.
And this is our slope.