Hey there! I'm happy to help!
Our mountain is at an elevation of 10,940. Our valley is at an elevation of -214 as it is below sea level, which is 0.
We want to find the difference. This means we subtract.
10940-(-214)=10940+214=11154
Therefore, there is an elevation difference if 11154 between the mountain and valley.
Have a wonderful day! :D