For the first one, first find your slope ([tex]m= \frac{y_2-y_1}{x_2-x_1} [/tex]), then use f(x)=mx+b. Your slope would be [tex]m= \frac{-5-5}{4-0} =-10/4=-5/2[/tex]. Your y-intercept is given as (0,5), so your equation of the line would be f(x)=(-5/2)x+5. For the second one, first you find what is constant. As your 3500 is a one time purchase, it is your constant, which will be your y-intercept. Your slope would be whatever changes over time, which is your maintenance cost of 125. This creates the equation f(x)=mx+b => f(x)=125x+3500.
