Answer
$B=0.0231c$
Work Step by Step
As the shifted wavelength $\lambda=525nm$ is longer than$\lambda_{\circ}=513nm$, therefore the galaxy is preceding the Earth.
We know that:
$\lambda=\lambda_{\circ}\sqrt\frac{1+B}{1-B}$
This can be simplified and rearranged as:
$\frac{1+B}{1-B}=(\frac{\lambda}{\lambda_{\circ}})^2$
We plug in the known vaues to obtain:
$\frac{1+B}{1-B}=(\frac{525}{513})^2=1.04733$
$B=0.0231c$
