| 108 | + | ( | k | − | 30 | − | k | ) | × | 18 5 | = | 72 | + | ( | k | − | 30 | − | k | ) | × | 12 5 |
| Left side of the equation = | 108 | + | k | × | 18 5 | − | 30 | × | 18 5 | − | k | × | 18 5 |
| = | 108 | + | k | × | 18 5 | − | 108 | − | k | × | 18 5 |
| = | 0 | + | 0 | k |
| 0 | + | 0 | k | = | 72 | + | ( | k | − | 30 | − | k | ) | × | 12 5 |
| Right side of the equation = | 72 | + | k | × | 12 5 | − | 30 | × | 12 5 | − | k | × | 12 5 |
| = | 72 | + | k | × | 12 5 | − | 72 | − | k | × | 12 5 |
| = | 0 | + | 0 | k |
| 0 | = | 0 |
| = | 0 | − | 0 |