$2-16-20:4$

= $2-16-5$

= $-14-5$

= $-19$

$\left(-79+18-16\right):\left(27-19-15\right)$

= $\left(-61-16\right):\left(8-15\right)$

= $-77:\left(-7\right)$

= $11$

$-11-\left(-6+10\right)-\left(-28:\left(-7\right)\right)$

= $-11-1·4-4$

= $-11-4-4$

= $-15-4$

= $-19$

$-2·\left(-13\right)+\left(12-6\right)·\left(-12\right):9$

= $26\left(-12\left(12-6\right)\right):9$

= $26+(-12·6):9$

= $26-72:9$

= $26-8$

= $18$