Current in a wire and compass needle

[choco_moo]

Homework Statement

A compass needle points 19.1 degrees E of N outdoors. However, when it is placed 9.80 cm to the east of a vertical wire inside a building, it points 55.7 degrees E of N. What is the magnitude of the current in the wire? The Earth's field there is 4.80×10-5 T and is horizontal.

Homework Equations

B = uI/(2*pi*r)

The Attempt at a Solution

Can someone point me in the right direction for this problem because I have no idea how to start. I'm pretty sure I have to use the Biot-Savart law, but I just don't know how to incorporate the angles given into the equation.

 

[inutard]

Try drawing a vector diagram of known fields (be sure to account for both the wire and the Earth in your diagram with correct angles in between).