Two engines pass each other moving in opposite directions with uniform speed of $30\;m/s$. One of them is blowing a whistle of frequency $540\; Hz$. Calculate the frequency heard by driver of second engine before they pass each other. Speed of sound is $330\; m/sec$

Question

$\begin{array}{1 1}(1) 540\;Hz \\ (2) 648\;Hz \\ (3) 270\;Hz \\ (4) 450\;Hz \end{array}$