The magnetic field due to a current loop at its center is given by the formula $B=\frac{\mu_0 I}{2R}$, where $I$ is the current, $R$ is the radius of the loop, and $\mu_0$ is the permeability of free space.
For the first loop, we have $B_1=\frac{\mu_0 I_1}{2R}$
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