The unit measure that is appropriate would be Cubic meters
I took 2 points from the graph and found my slope by using the slope formula, then I found my y-int which is the where the y crosses and that is -3. Hope this helps good luck !!
Answer: y=1/2x-3
Original price of book = x
Discount = 20%
Price at which meghan purchased it = $7

Original value of book was $8.75.
!! Hope It Helps !!