1) 
A : - 25 
B : - 10
C : 20 

2) A : - 30345 feet 
The change in elevation from the top of mount everest to the shore of  the dead land is -30,345 as to get to sea level from mouth everest would have an elevation of -29,035 feet and going under sea level to reach the shore if the dead land which is an elevation of -1,310 feet from sea level.