What is the elevation of the rest stop

Question

The hilltop is 130.5 feet above sea level. The valley floor is 46.5 feet below sea level. There is a scenic rest stop exactly halfway between the top of the hill and the valley floor. What is the elevation of the rest stop?

Answer 1

It is the mean of the 2 elevations, with above sea level positive, and below sea level negative (sea level = 0 elevation).

 

Hilltop:

 

y_h = 130.5 ft

 

Valley floor:  

 

y_v = -46.5 ft

 

y = (y_h + y_v) / 2 = [130.5 + (-46.5)] / 2 ft = 42 ft

 

The rest stop is 42 ft above sea level.