An electricity bill is a linear function with cost dependent on the number ofkwh(kilowatt hours) used in that particular month. In July you used800kwhand the bill was $109.50and in September you used600kwhand paid $85.50.Assume that cost andkwhused are linearly related.

a.Find the slope of the line between the two points in decimal form.

b. Find the y-intercept of the line (find b).

c.Write the equation of the line in slope intercept form (y =mx+ b).