$T=\frac{0.16 V }{\sum a s}$

Where $V$ is volume of hall in $m^3$

$\sum a s=a_1 s_1+a_2 s_2+\ldots \ldots=$ Total absorption of the hall (room)

Here $s_1, s_2, s_3 \ldots \ldots \ldots$ are surface area of the absorbers and $a_1, a_2, a_3 \ldots \ldots \ldots$ are their respective absorbption coefficients

$\frac{T^{\prime}}{T}=\frac{V^{\prime}}{s^{\prime}} \times \frac{s}{V}=\frac{(2)^3}{(2)^2}=\frac{8}{4}=2$

Hence, $T^{\prime}=2 T=2 \times 1=2\; s$.