Physics Questions? Really need some help!?

Question

I can't figure out how to set this problem up correctly. I thought that since each coil experienced the same maximum torque and received the same current that I could set their respective NIABsin(phi) equations equal to each other, cancel out current, and solve for the area of the second coil, but the answer that I got was incorrect (8.899 cm). Can anyone help me out in setting this problem up? Thanks in advance.

Here's the problem:

Two coils have the same number of circular turns and carry the same current. Each rotates in a magnetic field in a setup similar to the square coil in the figure below. Coil 1 has a radius of 4.2 cm and rotates in a 0.19 T field. Coil 2 rotates in a 0.42 T field. Each coil experiences the same maximum torque. What is the radius (in cm) of coil 2?

http://www.webassign.net/CJ/21-21.gif

Answer 1

Since every thing is the same except field and area B1A1=B2A2
(((4.2^2) * .19) / .42)^.5 = 2.82