What is carried by the waves? Mass,velocity,or energy?

The intensity of a sound wave while passing through an elastic medium falls by $10\%$ as it covers $1 \ m$ distance through the medium. If the initial intensity of the sound wave was $100 \ dB$,its value after it has passed through $3 \ m$ thickness of the medium will be .... $dB$.

Which of the following statements is correct?

The intensity level at a distance of $200 \ cm$ from a sound source is $80 \ dB$. If there is no loss of acoustic power in the air and the threshold intensity of hearing is $10^{-12} \ W/m^2$,what is the intensity level at a distance of $400 \ cm$ from the source (in $dB$)?

$A$ stone is dropped in still water,creating a circular wave pattern that spreads outward. If $r$ is the distance from the center of this circular pattern,the amplitude of the wave is proportional to ........

The intensity of sound after passing through a slab decreases by $30\%$. On passing through two such slabs,the intensity will decrease by ..... $\%$