As we have seen before, you can write the equation of any line in the form of y = mx + b . This is the so-called slope intercept form, because it gives you two important pieces of information: the slope m and the y-intercept b of the line. You can use these values for linear interpolation later.
If she works 40 hours or less then she earns 20x dollars. If she works more than 40 hours, then she earns 20×40 dollars for the first 40 hours and 30×(x-40) dollars for <span>every hour over 40 hours. The number of hours over 40 hours is x-40.</span>