| ( | X | × | 700 | + | ( | 10 | − | X | ) | × | 1200 | ) | × | 69 100 | − | ( | 10 | − | X | ) | × | 1080 | = | 420 |
| 方程左边 = | X | × | 700 | × | 69 100 | + | ( | 10 | − | X | ) | × | 1200 | × | 69 100 | − | ( | 10 | − | X | ) | × | 1080 |
| = | X | × | 483 | + | ( | 10 | − | X | ) | × | 828 | − | ( | 10 | − | X | ) | × | 1080 |
| = | 483 | X | + | 10 | × | 828 | − | X | × | 828 | − | ( | 10 | − | X | ) | × | 1080 |
| = | 483 | X | + | 8280 | − | X | × | 828 | − | ( | 10 | − | X | ) | × | 1080 |
| = | - | 345 | X | + | 8280 | − | ( | 10 | − | X | ) | × | 1080 |
| = | - | 345 | X | + | 8280 | − | 10 | × | 1080 | + | X | × | 1080 |
| = | - | 345 | X | + | 8280 | − | 10800 | + | X | × | 1080 |
| = | 735 | X | − | 2520 |
| 735 | X | − | 2520 | = | 420 |
| 735 | X | = | 420 | + | 2520 |
| 735 | X | = | 2940 |
| X | = | 2940 | ÷ | 735 |
| = | 2940 | × | 1 735 |
| = | 4 | × | 1 |
| X | = | 4 |