The slope is negative, which means the higher we price the trucks, the fewer we sell.

If we use the form y=mx +b for the line,

Then b = y – mx, where m is the slope, (-5)so B = 50000 +5(18000) = 140000

So Sales = 140000 – (5 * Price)

Just to check:

50,000 = 140000 – (5 * 18000) Yup

55,000 = 140000 – (5 * 17000) Yup

Note that the true behavior is only approximately linear. If we gave away trucks for free, we could give away a lot more than 140,000. If we sold the trucks for $28,000 each, we might sell one now and then.

(50000, 18000) and (55000, 17000)

Your slope, then, is (change in y)/(change in x) or

(17000 – 18000)/(55000 – 50000) =

-1000/5000 = -.2

This slope means that, for every additional truck you make beyond 50000, you’ll drop your price by .2 dollars per truck. The negative is what tells you that the price is dropping.

Note, please, that there are other ways to work this problem, with corresponding differences in the interpretation of the slope. One way to start figuring out what the slope means is to look at the units. In this case, we have “dollars” over “dollars per truck”. Since the slope is negative, that would translate to “lost dollars per dollars per truck”. Other examples might be more clear.

Hope this helps.