Plugging in the variables, you'd get 24 - (20-4) over (4 + 4). Add the contents of the parenthesis and you'd get 24 - (18)/(8). You'd divide, and get 24- 2.25, or 21.75.
If you aren't supposed to simplify on this assignment, it would probably be 24 - 18/8, or if you use fractions 21 and 3/4.
