homework and exercises - Magnitude of magnetic field at the center of circular wire

I'm preparing for an exam by solving the sample questions , here is the one I'm having difficulty with :

Following is the given circuit.
Which contains two resistance $R_1$ and $R_2$ in form of circle of radius $r = 1 m$ with a battery having e.m.f. $V = 10π $ volt.
Upper resistance is having resistivity $p_1 = 4$ & lower resistance having resistivity $p_2 = 2$.
Angle between two points $A$ and $B$ is $60°$. (wires have same cross section $A_1 = A_2 = 2 cm^2$)

Diagram :

Here is the question based on this passage that I'm having difficulty with :
Find magnitude of magnetic field at center.

(A) 0T (B) 1T (C) 2T (D) πT

The problem is I don't know any formula to calculate the magnetic field at a point nor am I expected to know (probably , at least it is not in syllabus) .

Also what is 'T' ? Is it unit of magnetic field?
The answer is 0 so I guess I should be able to reason why it should be 0 but I don't know how. Please help.