Answer
$86.9Hz$
Work Step by Step
We know that
$C=\frac{1}{\omega X_c}$
$\implies C=\frac{1}{[2\pi(57)](105)}=25.26\mu F$
Now we can find the required frequency as
$f^{\prime}=\frac{1}{2\pi CX_c^{\prime}}$
We plug in the known values to obtain:
$f^{\prime}=\frac{1}{2\pi(25.26)(72.5)}=86.9Hz$
