Dockjock
In the original post the Question gave the "True Track" as 180.
Think of this as the "track made good" along the ground.
If there was no wind then the "true track" would be the same as the "true Hdg" but we have 8R drift giving us the 180 true track or track along the ground measured in degrees true.
so lets remove the 8R from the true track and we are left with a true Hdg of 172. We know that the magnetic Hdg is 193 so the difference is the variation. 21w...
Hope that helps