8.2. Points $A, B, C, D$ are the centers of the circles inscribed in the faces $P Q S, P R S$, $Q R S$ and $P Q R$ of the tetrahedron $P Q R S$. It is known that $P Q=R S=7, P R=Q S=8, P S=Q R=9$. Find the volume of the tetrahedron $A B C D$. Round your answer to the nearest hundredth if necessary.
Answer: 1.84 (exact value: $\frac{5 \sqrt{11}}{9}$ ).