Each $*$ represents a missing operation. Work out what is that.

$9*15*\left(3*2\right)=12$

Calculate:

$\frac{7\times \sqrt{16}}{2^3+7^2-1}$

Calculate:

$\frac{5^2\times \sqrt{4}}{1+6^2-12}$

Calculate:

$\frac{2+3^2}{5^2+4\times 10-\sqrt{25}}$

Calculate:

$\frac{6^2-11}{2\left(17+2\times 4\right)}$

Calculate:

$\frac{3^2-3}{2\times \sqrt{81}}$

Calculate:

$\frac{3^2-5+6}{\sqrt{4}\times 5}$

Calculate:

$\frac{36-3\times \sqrt{16}}{15-3^2÷3}$

Calculate:

$\frac{-30+\left[18÷\left(3-12\right)+24\right]}{5-8-3^2}$