| 300 | × | 12 | a | = | 70000 | + | 40 | × | 12 | a |
| Left side of the equation = | 3600 | a |
| 3600 | a | = | 70000 | + | 40 | × | 12 | a |
| Right side of the equation = | 70000 | + | 480 | a |
| 3600 | a | = | 70000 | + | 480 | a |
| 3600 | a | − | 480 | a | = | 70000 |
| 3120 | a | = | 70000 |
| a | = | 70000 | ÷ | 3120 |
| = | 70000 | × | 1 3120 |
| = | 875 | × | 1 39 |
| a | = | 875 39 |
| a | = | 22.435897 |