Given that:
Times taken by Arjun $:T_{\text{car}} = 2 T_{\text{bus}}$
Speed of the car $ S_{\text{car}}= 40\:\text{km/hr}$
We know that, $\text{Speed} = \dfrac{\text{Distance}}{\text{Time}} $
Here, distance is constant,so $\text{Speed} \propto \dfrac{1}{\text{Time}}$
Now, $\dfrac{S_{\text{bus}}}{S_{\text{car}}} = \dfrac{T_{\text{car}}}{T_{\text{bus}}}$
$\implies \dfrac{S_{\text{bus}}}{40} = \dfrac{2T_{\text{bus}}}{T_{\text{bus}}}$
$\implies S_{\text{bus}} = 80\:\text{km/hr.}$
So, the correct answer is $(C).$
