Well in order to find differences, that means you have to subtract.
So if we take the lowest elevation (-1360) and subtract it from the highest elevation (29029) then we get 29029-(-1360)=30389 which equals the greatest elevation difference.
Now to get the least elevation difference then we take the two closest numbers and subtract them. In this case, the numbers would be (-344) and (-227)
So, (-344)-(-227)=(-117)
the greatest elevation difference is 30389 and the lowest elevation difference is (-117)