Anyone good at geometry???? (headings and bearings hw problem)

How do u do this problem??

A ship started at point a and traveled to point B on a heading of 120°. From point B the ship went on a heading of 43° to point C. Finally, the boat returned back to point A on a heading 257°. Find the measurement of each angle of the boats triangular path.

Picture of the triangle:
http://m.flickr.com/#/photos/68209979@N0…

It's a headings and bearings problem, this is a take home test and Our teacher barely explained it, can anyone help me? Or tell me how to start it??

Thank u soo so so much!!!

xx

draw 3 parallel lines trough each point A, B and C as we mark them on the paper. (I cannot visualize the attached link)

The heading is the angle of the direction vector with North vector.

< B = (180-120) + 43 = 103

< C = (360 - 257) - 43 = 60

< A = 180 - (103 + 60) = 17

Let N be a point infinity to the north and let S be a point at infinity to the south.

Angle NAB is 120° so angle ABN is the supplement of that, 60°, (interior angles on the same side of the transversal). Add that to angle NBC, 43°, and you have that the angle at B in the triangle is 103°.

Angle BCS must equal angle NBC (alternate interior angles) so it is 43°. Subtract 180° plus that from the bearing of 257° and you have the angle at C, 34°.

The angle at A must now be 43°.