From the figure;
The top part of the mountain is at an elevation of 264 units.
and from the hint the hikers are all at the same elevation; which again from the figure is given as 180 units.
So the difference in elevation for the hikers is: 264-180=84 units.
Hence; the answer is Option: A 84
Hope it helps...
Regards;
Leukonov/Olegion.