| 1600 | + | ( | 80 | − | x | ) | × | 10 | ( | 80 | − | x | ) | + | 40 | ( | 600 | − | 10 | ( | 80 | − | x | ) | ) | = | 9000 |
| 方程左边 = | 1600 | + | 80 | × | 10 | ( | 80 | − | x | ) | − | x | × | 10 | ( | 80 | − | x | ) | + | 40 | ( | 600 | − | 10 | ( | 80 | − | x | ) | ) |
| = | 1600 | + | 800 | ( | 80 | − | x | ) | − | x | × | 10 | ( | 80 | − | x | ) | + | 40 | ( | 600 | − | 10 | ( | 80 | − | x | ) | ) |
| = | 1600 | + | 800 | × | 80 | − | 800 | x | − | x | × | 10 | ( | 80 | − | x | ) | + | 40 | ( | 600 | − | 10 | ( | 80 | − | x | ) | ) |
| = | 1600 | + | 64000 | − | 800 | x | − | x | × | 10 | ( | 80 | − | x | ) | + | 40 | ( | 600 | − | 10 | ( | 80 | − | x | ) | ) |
| = | 65600 | − | 800 | x | − | x | × | 10 | ( | 80 | − | x | ) | + | 40 | ( | 600 | − | 10 | ( | 80 | − | x | ) | ) |
| = | 65600 | − | 800 | x | − | x | × | 10 | × | 80 | + | x | × | 10 | x | + | 40 | ( | 600 | − | 10 | ( | 80 | − | x | ) | ) |
| = | 65600 | − | 800 | x | − | x | × | 800 | + | x | × | 10 | x | + | 40 | ( | 600 | − | 10 | ( | 80 | − | x | ) | ) |
| = | 65600 | − | 1600 | x | + | x | × | 10 | x | + | 40 | ( | 600 | − | 10 | ( | 80 | − | x | ) | ) |
| = | 65600 | − | 1600 | x | + | x | × | 10 | x | + | 40 | × | 600 | − | 40 | × | 10 | ( | 80 | − | x | ) |
| = | 65600 | − | 1600 | x | + | x | × | 10 | x | + | 24000 | − | 400 | ( | 80 | − | x | ) |
| = | 89600 | − | 1600 | x | + | x | × | 10 | x | − | 400 | ( | 80 | − | x | ) |
| = | 89600 | − | 1600 | x | + | x | × | 10 | x | − | 400 | × | 80 | + | 400 | x |
| = | 89600 | − | 1600 | x | + | x | × | 10 | x | − | 32000 | + | 400 | x |
| = | 57600 | − | 1200 | x | + | x | × | 10 | x |
| 57600 | − | 1200 | x | + | x | × | 10 | x | = | 9000 |