| ( | ( | 220 | + | 260 | ) | × | 21 | − | X | ) | × | 9 10 | + | 18 | × | 21 | = | 9240 |
| Left side of the equation = | ( | ( | 220 | + | 260 | ) | × | 21 | − | X | ) | × | 9 10 | + | 378 |
| ( | ( | 220 | + | 260 | ) | × | 21 | − | X | ) | × | 9 10 | + | 378 | = | 9240 |
| Left side of the equation = | ( | 220 | + | 260 | ) | × | 21 | × | 9 10 | − | X | × | 9 10 | + | 378 |
| = | ( | 220 | + | 260 | ) | × | 189 10 | − | X | × | 9 10 | + | 378 |
| = | 220 | × | 189 10 | + | 260 | × | 189 10 | − | 9 10 | X | + | 378 |
| = | 4158 | + | 4914 | − | 9 10 | X | + | 378 |
| = | 9450 | − | 9 10 | X |
| 9450 | − | 9 10 | X | = | 9240 |
| - | 9 10 | X | = | 9240 | − | 9450 |
| - | 9 10 | X | = | - | 210 |
| 210 | = | 9 10 | X |
9 10 | X | = | 210 |
| X | = | 210 | ÷ | 9 10 |
| = | 210 | × | 10 9 |
| = | 70 | × | 10 3 |
| X | = | 700 3 |
| X | = | 233.333333 |