As the reaction is elementary, the rate of reaction is $r = K \cdot[ A ]^{2}\left[ B _{2}\right]$
on reducing the volume by a factor of $3,$ the concentrations of $A$ and $B _{2}$ will become $3$ times and hence, the rate becomes $3^{2} \times 3=27$ times of initial rate.
$\left[\right.$ આપેલ $\left.\mathrm{R}=8.314 \,\mathrm{JK}^{-1} \,\mathrm{~mol}^{-1}\right]$