Answered

What is the approximate distance between Portland, Oregon

(45° north, 122° west), and San Francisco, California (37° north, 122° west). Use 3,960 miles for the radius of Earth.

Verified Answer :

5669.71 km

Working
The two cities are located on the same longitude. 
The formula for the distance then is;
Distance = \(\frac{∅}{360}\)2π3960
where ∅ is the latitude difference-add the latitudes as they are on different sides.
Distance = \(\frac{82}{360}\)
2\(\frac{22}{7}\)3960
                =5669.71 km