Igot the answer but i need to know how did she get that answer

I'm terrible at math any here is appreciated.

Determine whether the set of whole numbers is closed under addition. explain why the set is or is not closed. give an example.

Answer asap ! the shortest path from point a to point b goes through a pond. to avoid the pond, you must walk straight 34 meters along one edge of the pond, then take a 90 degree turn, and again walk straight 41 meters along another edge of the pond to reach point b. about how many meters would be saved if it were possible to walk through the pond? a. 11 m b. 20 m c. 30.45 m d. 21.73 m