Evaluate 20 minus z when z equals negative 12.

1. Substitute negative 12 for z in the expression 20 minus z. 2. This gives 20 minus negative 12. 3. Subtracting a negative number is the same as adding, so 20 plus 12 equals 32. 4. Treating the double negative as if it stayed negative and writing 20 minus 12 instead gives the wrong value of 8. _Source: OpenStax Prealgebra (CC BY 4.0), Ch 3 "Integers", section 3.3 Subtract Integers_