To find the elevation of base camp, you start with Helene's initial elevation and then subtract the amount she descends.
Helene's starting elevation is 33 feet above sea level, and she descends 46 feet.
You can calculate the elevation of base camp as follows:
Elevation of base camp = Initial elevation - Descent Elevation of base camp = 33 feet - 46 feet Elevation of base camp = -13 feet
So, the elevation of base camp is 13 feet below sea level.