Answer:
2 1/4 yards above sea level
Step-by-step explanation:
The midpoint elevation is the average of the endpoint elevations, their sum divided by 2. When elevation is below sea level, it is represented by a negative number.
(17 3/4 - 13 1/4)/2 = (4 2/4)/2 = 2 1/4 . . . yards above sea level
