$(-2·\left(-8\right)):\left(-8:\left(-4\right)\right)$

= $16:2$

= $8$

$18·\left(-3\right):\left(-21-\left(-15\right)\right)$

= $-54:\left(-21+15\right)$

= $-54:\left(-6\right)$

= $9$

$18:\left(-11-\left(-14\right)\right)·\left(-6-\left(-3\right)\right)$

= $18:\left(-11+14\right)·\left(-6+3\right)$

= $18:3·\left(-3\right)$

= $6·\left(-3\right)$

= $-18$

$(-5·6-\left(-10\right)):\left((-20·5):\left(-10\right)\right)$

= $\left(-30+10\right):\left(-100:\left(-10\right)\right)$

= $-20:10$

= $-2$