| ( | - | 1 | ) | × | 3 | − | ( | l | − | 7 | ) | ÷ | 3 | × | ( | 3 | − | ( | - | 3 | ) | × | 2 | ) | = | 0 |
| Left side of the equation = | - | 1 | × | 3 | − | ( | l | − | 7 | ) | × | 1 3 | ( | 3 | − | ( | - | 3 | ) | × | 2 | ) |
| = | - | 3 | − | ( | l | − | 7 | ) | × | 1 3 | ( | 3 | − | ( | - | 3 | ) | × | 2 | ) |
| = | - | 3 | − | l | × | 1 3 | ( | 3 | − | ( | - | 3 | ) | × | 2 | ) | + | 7 | × | 1 3 | ( | 3 | − | ( | - | 3 | ) | × | 2 | ) |
| = | - | 3 | − | l | × | 1 3 | ( | 3 | − | ( | - | 3 | ) | × | 2 | ) | + | 7 3 | ( | 3 | − | ( | - | 3 | ) | × | 2 | ) |
| = | - | 3 | − | l | × | 1 3 | × | 3 | + | l | × | 1 3 | ( | - | 3 | ) | × | 2 | + | 7 3 | ( | 3 | − | ( | - | 3 | ) | × | 2 | ) |
| = | - | 3 | − | l | × | 1 | + | l | × | 2 3 | ( | - | 3 | ) | + | 7 3 | ( | 3 | − | ( | - | 3 | ) | × | 2 | ) |
| = | - | 3 | − | 1 | l | − | l | × | 2 3 | × | 3 | + | 7 3 | ( | 3 | − | ( | - | 3 | ) | × | 2 | ) |
| = | - | 3 | − | 1 | l | − | l | × | 2 | + | 7 3 | ( | 3 | − | ( | - | 3 | ) | × | 2 | ) |
| = | - | 3 | − | 3 | l | + | 7 3 | ( | 3 | − | ( | - | 3 | ) | × | 2 | ) |
| = | - | 3 | − | 3 | l | + | 7 3 | × | 3 | − | 7 3 | ( | - | 3 | ) | × | 2 |
| = | - | 3 | − | 3 | l | + | 7 | − | 14 3 | ( | - | 3 | ) |
| = | 4 | − | 3 | l | − | 14 3 | ( | - | 3 | ) |
| = | 4 | − | 3 | l | + | 14 3 | × | 3 |
| = | 4 | − | 3 | l | + | 14 |
| = | 18 | − | 3 | l |
| 18 | − | 3 | l | = | 0 |
| - | 3 | l | = | 0 | − | 18 |
| - | 3 | l | = | - | 18 |
| 18 | = | 3 | l |
| 3 | l | = | 18 |
| l | = | 18 | ÷ | 3 |
| = | 18 | × | 1 3 |
| = | 6 | × | 1 |
| l | = | 6 |