| ( | ( | X | × | 700 | + | ( | 10 | − | X | ) | × | 1200 | ) | × | 69 100 | − | ( | 10 | − | X | ) | × | 1080 | ) | ÷ | X | = | 420 |
| Multiply both sides of the equation by: | X |
| ( | ( | X | × | 700 | + | ( | 10 | − | X | ) | × | 1200 | ) | × | 69 100 | − | ( | 10 | − | X | ) | × | 1080 | ) | = | 420 | X |
| ( | X | × | 700 | + | ( | 10 | − | X | ) | × | 1200 | ) | × | 69 100 | − | ( | 10 | − | X | ) | × | 1080 | = | 420 | X |
| X | × | 700 | × | 69 100 | + | ( | 10 | − | X | ) | × | 1200 | × | 69 100 | − | ( | 10 | − | X | ) | × | 1080 | = | 420 | X |
| X | × | 483 | + | ( | 10 | − | X | ) | × | 828 | − | ( | 10 | − | X | ) | × | 1080 | = | 420 | X |
| 483 | X | + | 10 | × | 828 | − | X | × | 828 | − | ( | 10 | − | X | ) | × | 1080 | = | 420 | X |
| 483 | X | + | 8280 | − | X | × | 828 | − | ( | 10 | − | X | ) | × | 1080 | = | 420 | X |
| - | 345 | X | + | 8280 | − | ( | 10 | − | X | ) | × | 1080 | = | 420 | X |
| - | 345 | X | + | 8280 | − | 10 | × | 1080 | + | X | × | 1080 | = | 420 | X |
| - | 345 | X | + | 8280 | − | 10800 | + | X | × | 1080 | = | 420 | X |
| 735 | X | − | 2520 | = | 420 | X |
| 735 | X | − | 420 | X | = | 2520 |
| 315 | X | = | 2520 |
| X | = | 2520 | ÷ | 315 |
| = | 2520 | × | 1 315 |
| = | 8 | × | 1 |
| X | = | 8 |