An observer is moving with half the speed of light towards stationary microwave source emitting waves at frequency $10\;GHz$. What is the frequency of the microwave measured by the observer ? (speed of light = $3 \times 10^8\;ms^{–1}$ )

Question

( A ) 15.3 GHz
( B ) 17.3 GHz
( C ) 12.1 GHz
( D ) 10.1 GHz