Assuming the earth is a sheet of radius 6378 km, what is the difference in latitude (in degrees) of two cities, one of which is 600 km due north of the other?
I think I'll assume it is a sphere of radius 6378 km.
In that case, each degree of latitude is
1/360 * 2π * 6378 = 111.317 km
so your cities are
600/111.317 = 5.39° apart