| ( | 900 | + | X | ) | ÷ | 85 | = | ( | 1800 | + | X | ) | ÷ | 160 |
| 方程左边 = | 900 | × | 1 85 | + | X | × | 1 85 |
| = | 180 17 | + | X | × | 1 85 |
180 17 | + | 1 85 | X | = | ( | 1800 | + | X | ) | ÷ | 160 |
| 方程右边 = | 1800 | × | 1 160 | + | X | × | 1 160 |
| = | 45 4 | + | X | × | 1 160 |
180 17 | + | 1 85 | X | = | 45 4 | + | 1 160 | X |
1 85 | X | − | 1 160 | X | = | 45 4 | − | 180 17 |
3 544 | X | = | 45 4 | − | 180 17 |
3 544 | X | = | 45 68 |
| X | = | 45 68 | ÷ | 3 544 |
| = | 45 68 | × | 544 3 |
| = | 15 | × | 8 |
| X | = | 120 |