Answer
The elevation of the helicopter = +10.75 meters
Step-by-step explanation
Before starting, note that
18 1/2 = 18.50
-7 3/4 = -7.75
And the ground has an elevation of 0, spots above the ground have positive elevations and spots below the ground have negative elevation.
Let the elevation of the helicopter be x.
And the elevation of the submarine be y.
The difference in elevation of a helicopter and a submarine is 18.50 meter
x - y = 18.50
Elevation of a submarine is -7.75 meters (there's negative sign in front because a submarine is under the sea level)
So, y = -7.75
Recall that
x - y = 18.50
x - (-7.75) = 18.50
x + 7.75 = 18.50
x = 18.50 - 7.75
x = +10.75 m
The elevation of the helicopter = +10.75 meters
Hope this Helps!!!