The sea level is considered to have an elevation of zero feet.
To determine which checkpoint is furthest away from the sea level you have to calculate their absolute difference to zero and compare them:
Checkpoint A
Checkpoint B
Checkpoint C
Checkpoint D
Checkpoint E
Ordered from closest to furthest the distance of each checkpoint from sea level is:
[tex]0The furthest checkpoint to sea level is Checkpoint E, which is 18.5ft away