I need to prove that the magnetic force done to a square loop with a current by an uniform magnetic field is zero. The exact problem is this:

I'm pretty sure you can calculate the force on a wire segment with F=(current through wire)(length of wire)x(magnetic field). Can I apply that in this problem or would a different approach be more suitable? The problem also states that I need to calculate a torque, I honestly have no idea WHERE I can do that in this problem.