| ( | 200 | − | 156 | − | X | ) | ( | 20 | + | 5 | X | ) | = | 1600 |
| 方程左边 = | 200 | ( | 20 | + | 5 | X | ) | − | 156 | ( | 20 | + | 5 | X | ) | − | X | ( | 20 | + | 5 | X | ) |
| = | 200 | × | 20 | + | 200 | × | 5 | X | − | 156 | ( | 20 | + | 5 | X | ) | − | X | ( | 20 | + | 5 | X | ) |
| = | 4000 | + | 1000 | X | − | 156 | ( | 20 | + | 5 | X | ) | − | X | ( | 20 | + | 5 | X | ) |
| = | 4000 | + | 1000 | X | − | 156 | × | 20 | − | 156 | × | 5 | X | − | X | ( | 20 | + | 5 | X | ) |
| = | 4000 | + | 1000 | X | − | 3120 | − | 780 | X | − | X | ( | 20 | + | 5 | X | ) |
| = | 880 | + | 220 | X | − | X | ( | 20 | + | 5 | X | ) |
| = | 880 | + | 220 | X | − | X | × | 20 | − | X | × | 5 | X |
| = | 880 | + | 200 | X | − | X | × | 5 | X |
| 880 | + | 200 | X | − | X | × | 5 | X | = | 1600 |