Hey jaxta.

The bearing is going to be the number of degrees in a clock-wise direction from the north. If angles at a point add up to 360 degrees, then you can add up the angles from the north on-wards to get the bearing.

If you are given a bearing from the left you take away the angle formed in the triangle and if you are given a bearing from the left you add the angle.

Have you been given any existing bearings? If so take a look at whether they are to the right or left of bearing AD and subtract or add (depending on whether its to left or right) the appropriate angle and you will have your bearing.