The magnetic flux (\(\phi\)) through loop B due to current in loop A is given by:
\[ \phi = M \cdot i = B \cdot A \]
The mutual inductance is:
\[ M = \frac{\mu_0 \pi a^2}{2b} \]
where \(a\) is the radius of loop A, \(b\) is the distance between the loops, and \(\mu_0\) is the permeability of free space.