Parallel equations have identical or equal slopes. Given the form of the equation; y=5x+b and the point it passes through (8,-2) we determine the unknown value b by substituting x with 8 and y with -2. We solve the equation; -2 =5(8)+b to obtain b = -42
The slope would be 4.33. He sells 13 cars in 3 months, 13/3=4.33 cars each month. While you can't sell 4.33, remember that this is just the slope. The equation would be apprx y=4.33(x)