Kevin starts a new job in sales next month. He will earn $800 per month plus a certain amount for each shirt he sells. The graph below shows the amount Kevin will earn per month based on how many shirts he sells. Find the equation of this line where is the amount he earns for selling number of shirts.

Question

Kevin starts a new job in sales next month. He will earn $800 per month plus a certain amount for each shirt he sells. The graph below shows the amount Kevin will earn per month based on how many shirts he sells.  Find the equation of this line where  is the amount he earns for selling  number of shirts.

Quizplus · Accepted Answer

Using the two given points on the line (0,800) and (40,2000), we can calculate the slope of the line:
slope = (2000-800)/(40-0) = 30

Then we can use the point-slope form of a line to find the equation:
y - y1 = m(x - x1)    where (x1,y1) is either of the given points on the line
y - 800 = 30(x - 0)
y = 30x + 800

So the equation of the line is y = 30x + 800, and plugging in x=11 gives us choice B: 
y = 30(11) + 800 = $1,130

Kevin Starts a New Job in Sales Next Month