Hi David,

To find the cost of an additional square foot, you need to calculate the approximate slope of the data shown in the scatterplot. The trend is clearly linear, so looking towards the bottom left of the scatterplot you might calculate the slope as follows:

(250,000 - 150,000) / (2000 - 1000) = (100,000 / 1000) = 100

So $80 is the most reasonable approximation based on the above calculation.

I hope this helps! Please let me know if you have any further questions!