How to determine the longitude of an object located on the meridian?

1) Choose the meridian you need.
2) Find the points of contact of this object with it.
3) Find the coordinates of these points.
4) Calculate the distance in degrees.
a) If the points are in one hemisphere, then we add.
b) If the points are in different hemispheres, then subtracts the smaller from the larger.
5) Multiply the resulting number by 11 km, because. in one degree along the meridian (any) is 111 km.