5 4 | × | 144 | + | 30 | ( | t | − | 12 | ) | = | 20 | t |
| Left side of the equation = | 180 | + | 30 | ( | t | − | 12 | ) |
| 180 | + | 30 | ( | t | − | 12 | ) | = | 20 | t |
| Left side of the equation = | 180 | + | 30 | t | − | 30 | × | 12 |
| = | 180 | + | 30 | t | − | 360 |
| = | - | 180 | + | 30 | t |
| - | 180 | + | 30 | t | = | 20 | t |
| 30 | t | − | 20 | t | = | 180 |
| 10 | t | = | 180 |
| t | = | 180 | ÷ | 10 |
| = | 180 | × | 1 10 |
| = | 18 | × | 1 |
| t | = | 18 |