What’s the correct answer for this?

Revising:

re-examine and make alterations to (written or printed matter).

or

reconsider and amend (something), especially in the light of further evidence or to reflect a changed situation.

Similar words:

-amend

-correct

-change

-adapt

or

-reconsider

-review

onto a large boat, and mark the water level that the boat sinks to. then, take the elephant out and put a bunch of marked weights onto the boat until it reaches the same water level. add up the masses of the weights to get the weight of the elephant.