| x | ( | 180 | × | 9 5 | ) | + | ( | 80 | − | x | ) | ( | 120 | × | 3 2 | ) | = | 18720 |
| 方程左边 = | x | × | 180 | × | 9 5 | + | ( | 80 | − | x | ) | ( | 120 | × | 3 2 | ) |
| = | x | × | 324 | + | ( | 80 | − | x | ) | ( | 120 | × | 3 2 | ) |
| = | 324 | x | + | 80 | ( | 120 | × | 3 2 | ) | − | x | ( | 120 | × | 3 2 | ) |
| = | 324 | x | + | 80 | × | 120 | × | 3 2 | − | x | ( | 120 | × | 3 2 | ) |
| = | 324 | x | + | 14400 | − | x | ( | 120 | × | 3 2 | ) |
| = | 324 | x | + | 14400 | − | x | × | 120 | × | 3 2 |
| = | 324 | x | + | 14400 | − | x | × | 180 |
| = | 144 | x | + | 14400 |
| 144 | x | + | 14400 | = | 18720 |
| 144 | x | = | 18720 | − | 14400 |
| 144 | x | = | 4320 |
| x | = | 4320 | ÷ | 144 |
| = | 4320 | × | 1 144 |
| = | 30 | × | 1 |
| x | = | 30 |