| 1 | − | a | × | 10 | ÷ | 1 | − | a | × | 30 | = | 1 | ÷ | 12 |
| Left side of the equation = | 1 | − | a | × | 10 | − | a | × | 30 |
| = | 1 | − | 40 | a |
| 1 | − | 40 | a | = | 1 | ÷ | 12 |
| Right side of the equation = | 1 12 |
| 1 | − | 40 | a | = | 1 12 |
| - | 40 | a | = | 1 12 | − | 1 |
| - | 40 | a | = | - | 11 12 |
11 12 | = | 40 | a |
| 40 | a | = | 11 12 |
| a | = | 11 12 | ÷ | 40 |
| = | 11 12 | × | 1 40 |
| a | = | 11 480 |
| a | = | 0.022917 |