The expression is 

Additive inverse of – 4 is 4.

To subtract – 4, add 4.

Now, the expression becomes .

To add integers first draw a number line diagram.

\
• Start from zero move 16 units right to reach 16.
\
• Then move 4 units right show the addition of 4.
\
• Find the final position on the number line.
\

The difference of is 20.

The difference of is 20.