This is a simple equation:)
We have to isolate "n" to be alone.
-21 = n - 8
First add 8 to both sides.
-21 = n - 8
+8 = + 8 it cancels out on the right side of the equal side and you solve on the left side
soooo
-21 + 8 = -13
-13 = n
Finally our answer is
-13 = n
When in doubt, eat a pineapple:)