The Doppler effect for light causes a photon emitted with wavelength $\lambda_0$ to be detected with wavelength
$\begin{align*}\lambda = \lambda_0 \sqrt{\frac{c + v}{c - v}}\end{align*}$
where $v$ is the relative velocity of the source and the observer. This equation can be solved for $v$ as follows.
$\begin{align*}& & \frac{\lambda}{\lambda_0} &= \sqrt{\frac{c + v}{c - v}} \\&\Longrightarrow&\frac{4}{3} ...$
Therefore, answer (A) is correct.

Solution to 2008 Problem 55