In practice,kidneys are often rationed on the basis of willingness to pay,and many recipients pay most or all of the $40000 price that clears the market when supply is constrained.Rectangles A and D measure the total value of kidneys when supply is constrained.In practice, kidneys are often rationed on the basis of willingness to pay, and many recipients pay most or all of the $40000 price that clears the market when supply is constrained. Rectangles A and D measure the total value of kidneys when supply is constrained