4 ÷ 6/9 is also equal to 4 x 9/6. This is because when you divide by a fraction, you change the division sign to multiply and reverse the numerator and the denominator of the fraction. For example, if x/y was a fraction, it would become y/x. THIS IS ONLY DURING DIVISION!
So, we now that 4 ÷ 6/9 is equal to 4 x 9/6. 4 x 9/6 = (4x9)/6 = 36/6 = 6.
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)