| 15 | − | 3 | ( | 4 | + | 2 | x | ) | + | 5 | ( | 7 | + | 3 | x | ) | = | 21 |
| Left side of the equation = | 15 | − | 3 | × | 4 | − | 3 | × | 2 | x | + | 5 | ( | 7 | + | 3 | x | ) |
| = | 15 | − | 12 | − | 6 | x | + | 5 | ( | 7 | + | 3 | x | ) |
| = | 3 | − | 6 | x | + | 5 | ( | 7 | + | 3 | x | ) |
| = | 3 | − | 6 | x | + | 5 | × | 7 | + | 5 | × | 3 | x |
| = | 3 | − | 6 | x | + | 35 | + | 15 | x |
| = | 38 | + | 9 | x |
| 38 | + | 9 | x | = | 21 |
| 9 | x | = | 21 | − | 38 |
| 9 | x | = | - | 17 |
| x | = | - | 17 | ÷ | 9 |
| = | - | 17 | × | 1 9 |
| x | = | - | 17 9 |
| x | = | - 1.888889 |