| 80 | ( | x | − | 5 | ) | = | 50 | ( | x | + | 4 | ) |
| Left side of the equation = | 80 | x | − | 80 | × | 5 |
| = | 80 | x | − | 400 |
| 80 | x | − | 400 | = | 50 | ( | x | + | 4 | ) |
| Right side of the equation = | 50 | x | + | 50 | × | 4 |
| = | 50 | x | + | 200 |
| 80 | x | − | 400 | = | 50 | x | + | 200 |
| 80 | x | − | 50 | x | = | 200 | + | 400 |
| 30 | x | = | 200 | + | 400 |
| 30 | x | = | 600 |
| x | = | 600 | ÷ | 30 |
| = | 600 | × | 1 30 |
| = | 20 | × | 1 |
| x | = | 20 |