Since it says that the two variables are linear, you know that they graph into a straight line. Also, you are given two points on that line, so you can find the slope (without graphing).

Slope is change in y divided by change in x

given points (10,000, 100,000 ) and (50,000, 200,000), the slope is (200000-1000000)/ (50000 – 10000) or can be reduced to 5/2

Using the slope intercept formula for a line, y=mx+b, you know that the equation takes the form y = (5/2)x + b

Now, plug in the intercepts for one of the two points to find b.

100000 = (5/2)10000 + b Solving you get b = 75000

Now you have the equation y = (5/2)x + 75000

where y is number of boxes sold and x is advertising money spent. You can verify that the equation works by plugging in the other point you are given: 200000 = (5/2)50000 + 75000 which works!

Hope this helps