Calculating Implementation Shortfall is like...

Parallel parking in the city. I always get it right, but I have no idea how I did it.

this is SPOT ON

the reason is because we calculate is the easy way. as in (paper port terminal value minus paper port cost) -(actual port terminal value-actual port cost)/ paper port cost

this is one of the few problems in the curriculum where it is easier to solve the whole problem set rather than just 1 component.