| 800 | ( | 100 | − | x | ) | = | ( | 80 | − | x | ) | × | 1800 |
| Left side of the equation = | 800 | × | 100 | − | 800 | x |
| = | 80000 | − | 800 | x |
| 80000 | − | 800 | x | = | ( | 80 | − | x | ) | × | 1800 |
| Right side of the equation = | 80 | × | 1800 | − | x | × | 1800 |
| = | 144000 | − | x | × | 1800 |
| 80000 | − | 800 | x | = | 144000 | − | 1800 | x |
| - | 800 | x | + | 1800 | x | = | 144000 | − | 80000 |
| 1000 | x | = | 144000 | − | 80000 |
| 1000 | x | = | 64000 |
| x | = | 64000 | ÷ | 1000 |
| = | 64000 | × | 1 1000 |
| = | 64 | × | 1 |
| x | = | 64 |