| 100 | a | + | 120 | ( | 300 | − | a | ) | = | 33000 |
| Left side of the equation = | 100 | a | + | 120 | × | 300 | − | 120 | a |
| = | 100 | a | + | 36000 | − | 120 | a |
| = | - | 20 | a | + | 36000 |
| - | 20 | a | + | 36000 | = | 33000 |
| - | 20 | a | = | 33000 | − | 36000 |
| - | 20 | a | = | - | 3000 |
| 3000 | = | 20 | a |
| 20 | a | = | 3000 |
| a | = | 3000 | ÷ | 20 |
| = | 3000 | × | 1 20 |
| = | 150 | × | 1 |
| a | = | 150 |