First I found the slope by using the the definition that slope is rise/run so I saw that the y value went up from 4 to 9 which is 5 units and then the x value went up one in that same time. This means that the slope is 5/1. Then I found the y intercept by seeing where x = 0. On the graph you can see the line touches the y - axis at a value of 4 which means that the y - intercept is 4. Plugging these values into the y = mx + b equation you get y = 5x + 4.
If the CD is $17 and is have a 20% off then you multiply .20 and 17 to get the amount that is off. Subtract that answer from 17 and you should get $13.60. That is the cost of the CD WITHOUT tax. To apply the tax, you multiply the cost and 0.05 (5%) to get 0.68. 0.68 is the tax cost. To get the entire cost of the CD, you add 0.68 (tax) and price (13.60) and get $14.28.
