| 30 | × | 0 | + | 40 | x | = | ( | 30 | − | x | ) | × | 60 |
| Left side of the equation = | 0 | + | 40 | x |
| 0 | + | 40 | x | = | ( | 30 | − | x | ) | × | 60 |
| Right side of the equation = | 30 | × | 60 | − | x | × | 60 |
| = | 1800 | − | x | × | 60 |
| 40 | x | = | 1800 | − | 60 | x |
| 40 | x | + | 60 | x | = | 1800 |
| 100 | x | = | 1800 |
| x | = | 1800 | ÷ | 100 |
| = | 1800 | × | 1 100 |
| = | 18 | × | 1 |
| x | = | 18 |