$\"\"$

The expression is $\"\"$ .

$\"\"$ (Substitute y = 8 and z = – 12 in original expression) $\"\"$

Additive inverse of – 8 is 8.

To subtract – 8, add 8.

Now, the expression becomes $\"\"$ .

$\"\"$ (Add: $\"\"$ ) $\"\"$

The simplified expression is – 20.