The initial elevation of the hike can be represented as -20 meters, this is because the initial elevation is below the sea level, and in terms of elevation the sea level is considered to be 0. Now, using this number the final elevation can be calculated by adding the two numbers:
-20 + 3400 = 3380
This implies the final elevation has 3380 meters
You can also get this same result by considering there are 20 meters from the initial elevation to the sea level and then 3380 meters from the sea level to the final elevation (3380+20 = 3400).
