| x | = | 7800000 | − | ( | 10 | × | 40 | × | 4 | ) | ÷ | ( | ( | 40 | + | 10 | ) | × | 10 | ) |
| 方程两边同时乘以: | ( | ( | 40 | + | 10 | ) | × | 10 | ) |
| x | ( | ( | 40 | + | 10 | ) | × | 10 | ) | = | 7800000 | ( | ( | 40 | + | 10 | ) | × | 10 | ) | − | ( | 10 | × | 40 | × | 4 | ) |
| x | ( | 40 | + | 10 | ) | × | 10 | = | 7800000 | ( | ( | 40 | + | 10 | ) | × | 10 | ) | − | ( | 10 | × | 40 | × | 4 | ) |
| x | ( | 40 | + | 10 | ) | × | 10 | = | 7800000 | ( | 40 | + | 10 | ) | × | 10 | − | ( | 10 | × | 40 | × | 4 | ) |
| x | ( | 40 | + | 10 | ) | × | 10 | = | 78000000 | ( | 40 | + | 10 | ) | − | ( | 10 | × | 40 | × | 4 | ) |
| x | × | 40 | × | 10 | + | x | × | 10 | × | 10 | = | 78000000 | ( | 40 | + | 10 | ) | − | ( | 10 | × | 40 | × | 4 | ) |
| x | × | 40 | × | 10 | + | x | × | 10 | × | 10 | = | 78000000 | × | 40 | + | 78000000 | × | 10 | − | ( | 10 | × | 40 | × | 4 | ) |
| x | × | 400 | + | x | × | 100 | = | 3120000000 | + | 780000000 | − | ( | 10 | × | 40 | × | 4 | ) |
| 500 | x | = | 3900000000 | − | ( | 10 | × | 40 | × | 4 | ) |
| 500 | x | = | 3900000000 | − | 10 | × | 40 | × | 4 |
| 500 | x | = | 3900000000 | − | 1600 |
| 500 | x | = | 3899998400 |
| x | = | 3899998400 | ÷ | 500 |
| = | 3899998400 | × | 1 500 |
| = | 38999984 | × | 1 5 |
| x | = | 38999984 5 |
| x | = | 7799996.8 |