| 40 | ( | x | + | 8 | ) | − | 100 | = | 400 | × | 3 20 |
| Left side of the equation = | 40 | x | + | 40 | × | 8 | − | 100 |
| = | 40 | x | + | 320 | − | 100 |
| = | 40 | x | + | 220 |
| 40 | x | + | 220 | = | 400 | × | 3 20 |
| Right side of the equation = | 60 |
| 40 | x | + | 220 | = | 60 |
| 40 | x | = | 60 | − | 220 |
| 40 | x | = | - | 160 |
| x | = | - | 160 | ÷ | 40 |
| = | - | 160 | × | 1 40 |
| = | - | 4 | × | 1 |
| x | = | - | 4 |