To calculate the magnetic bearing, you would subtract the declination from the true bearing if the declination is east, or add the declination if the declination is west. In this case, since the declination is 8 degrees east, you would subtract the declination from the true bearing of 180 degrees.

Magnetic bearing = True bearing - Declination Magnetic bearing = 180 degrees - 8 degrees Magnetic bearing = 172 degrees

No

Assuming the subject is magnetic declination the difference between the north pole and the true north pole this difference, is the magnetic declination, there is not information on what purpose it serves.

Magnetic Declination

+15° 45'