# Acoustics exercise

I have been asked to solve this exercise.

An environment of $V=1500$ $m^3$, it is considered a reverberated field acoustic pressure level of $70$ $dB$ when an acoustic source of $80$ $dB$ is activated. Compute the total absorption (in $m^2$) in order to obtain a reverberation time of $4$ seconds.

Let me show you my idea: I have to use Sabine's formula $$T_{60} = \beta \frac{V}{A} \text{ with } \beta=0.16$$

The surface $A$ should be computed as

$$A = \sum_i a_i S_i$$

where $a_i$ is the absorption coefficient of the $i$-th surface $S_i$.

Can someone help me to find the missing surfaces and coefficients because I can't understand in which way I must find them?