| 80 | × | 9 10 | = | 80 | × | 60 | + | ( | X | − | 60 | ) | × | 4 5 |
| Left side of the equation = | 72 |
| 72 | = | 80 | × | 60 | + | ( | X | − | 60 | ) | × | 4 5 |
| Right side of the equation = | 4800 | + | ( | X | − | 60 | ) | × | 4 5 |
| 72 | = | 4800 | + | ( | X | − | 60 | ) | × | 4 5 |
| Right side of the equation = | 4800 | + | X | × | 4 5 | − | 60 | × | 4 5 |
| = | 4800 | + | X | × | 4 5 | − | 48 |
| = | 4752 | + | 4 5 | X |
| 72 | = | 4752 | + | 4 5 | X |
| - | 4 5 | X | = | 4752 | − | 72 |
| - | 4 5 | X | = | 4680 |
| - | 4680 | = | 4 5 | X |
4 5 | X | = | - | 4680 |
| X | = | - | 4680 | ÷ | 4 5 |
| = | - | 4680 | × | 5 4 |
| = | - | 1170 | × | 5 |
| X | = | - | 5850 |