If +42 represents 42m above the water surface, what does each of the following represent: [4 MARKS]
(i) −87+55
(ii) +98−115
(ii) +36+57−73
(iv) −42−23+39
Each point: 1 Mark
(i) −87+55=−32
⇒32m below the water surface
(ii) +98−115=−17
⇒17m below the water surface
(ii) +36+57−73=20
⇒20m above the water surface
(iv) −42−23+39=−26
⇒26m below the water surface