Answer:
4 - ( 3x - 8 ) = 21
break the bracket first ,it gives : 4 - 3x + 8 = 21
12 - 3x = 21
- 3x = 21 - 12
- 3x = 9
-x = 9/3
-x = 3
X = - 3
[ check if the answer is correct, put -3 instead of X in the above equation ! we get 4 - { 3(-3) - 8 } = 21
4 - { - 9 - 8 } = 21
4 - { - 17 } = 21
break the bracket, minus and minus will multiply and will become plus , so we have 4 + 17 = 21 , hence 21 = 21 ! therefore X = -3