| 4200 | ( | x | − | 50 | ) | = | 900 | ( | 160 | − | x | ) |
| Left side of the equation = | 4200 | x | − | 4200 | × | 50 |
| = | 4200 | x | − | 210000 |
| 4200 | x | − | 210000 | = | 900 | ( | 160 | − | x | ) |
| Right side of the equation = | 900 | × | 160 | − | 900 | x |
| = | 144000 | − | 900 | x |
| 4200 | x | − | 210000 | = | 144000 | − | 900 | x |
| 4200 | x | + | 900 | x | = | 144000 | + | 210000 |
| 5100 | x | = | 144000 | + | 210000 |
| 5100 | x | = | 354000 |
| x | = | 354000 | ÷ | 5100 |
| = | 354000 | × | 1 5100 |
| = | 1180 | × | 1 17 |
| x | = | 1180 17 |
| x | = | 69.411765 |