| ( | 4000 | + | 3 | a | − | 8000 | ) | × | 10 100 | + | 3000 | × | 3 100 | = | 200 |
| Left side of the equation = | ( | 4000 | + | 3 | a | − | 8000 | ) | × | 10 100 | + | 90 |
| ( | 4000 | + | 3 | a | − | 8000 | ) | × | 10 100 | + | 90 | = | 200 |
| Left side of the equation = | 4000 | × | 10 100 | + | 3 | a | × | 10 100 | − | 8000 | × | 10 100 | + | 90 |
| = | 400 | + | 3 10 | a | − | 800 | + | 90 |
| = | - | 310 | + | 3 10 | a |
| - | 310 | + | 3 10 | a | = | 200 |
3 10 | a | = | 200 | + | 310 |
3 10 | a | = | 510 |
| a | = | 510 | ÷ | 3 10 |
| = | 510 | × | 10 3 |
| = | 170 | × | 10 |
| a | = | 1700 |