| 72 | + | ( | k | − | 30 | + | k | ) | × | 18 5 | + | ( | k | − | 30 | + | k | ) | × | 12 5 | = | 108 | + | ( | k | − | 30 | + | k | ) | × | 18 5 | × | 2 |
| Left side of the equation = | 72 | + | k | × | 18 5 | − | 30 | × | 18 5 | + | k | × | 18 5 | + | ( | k | − | 30 | + | k | ) | × | 12 5 |
| = | 72 | + | k | × | 18 5 | − | 108 | + | k | × | 18 5 | + | ( | k | − | 30 | + | k | ) | × | 12 5 |
| = | - | 36 | + | 36 5 | k | + | ( | k | − | 30 | + | k | ) | × | 12 5 |
| = | - | 36 | + | 36 5 | k | + | k | × | 12 5 | − | 30 | × | 12 5 | + | k | × | 12 5 |
| = | - | 36 | + | 36 5 | k | + | k | × | 12 5 | − | 72 | + | k | × | 12 5 |
| = | - | 108 | + | 12 | k |
| - | 108 | + | 12 | k | = | 108 | + | ( | k | − | 30 | + | k | ) | × | 18 5 | × | 2 |
| Right side of the equation = | 108 | + | ( | k | − | 30 | + | k | ) | × | 36 5 |
| - | 108 | + | 12 | k | = | 108 | + | ( | k | − | 30 | + | k | ) | × | 36 5 |
| Right side of the equation = | 108 | + | k | × | 36 5 | − | 30 | × | 36 5 | + | k | × | 36 5 |
| = | 108 | + | k | × | 36 5 | − | 216 | + | k | × | 36 5 |
| = | - | 108 | + | 72 5 | k |
| - | 108 | + | 12 | k | = | - | 108 | + | 72 5 | k |
| 12 | k | − | 72 5 | k | = | - | 108 | + | 108 |
| - | 12 5 | k | = | - | 108 | + | 108 |
| - | 12 5 | k | = | - | 0 |
| 0 | = | 12 5 | k |
12 5 | k | = | 0 |
| k | = | 0 | ÷ | 12 5 |
| = | 0 | × | 5 12 |
| k | = | 0 |