The line of best fit is the line that best fits the data / points. This line is already graphed for us, nice!
To find how much we should purchase if we only want to buy $5.05, we look to the y-axis (cost of each box of paper) and locate 5.05, in between the 5 and the 5.1. We look across to the x-axis (number of boxes) and see the answer is 3.5.
Have a nice day!
I hope this is what you are looking for, but if not - comment! I will edit and update my answer accordingly. (ノ^∇^)
