| ( | x | − | 80 | ) | ( | 1 | − | 25 100 | ) | ÷ | 4200 | = | 0 |
| Left side of the equation = | x | ( | 1 | − | 25 100 | ) | × | 1 4200 | − | 80 | ( | 1 | − | 25 100 | ) | × | 1 4200 |
| = | x | ( | 1 | − | 25 100 | ) | × | 1 4200 | − | 2 105 | ( | 1 | − | 25 100 | ) |
| = | x | × | 1 | × | 1 4200 | − | x | × | 25 100 | × | 1 4200 | − | 2 105 | ( | 1 | − | 25 100 | ) |
| = | x | × | 1 4200 | − | x | × | 1 16800 | − | 2 105 | ( | 1 | − | 25 100 | ) |
| = | 1 5600 | x | − | 2 105 | ( | 1 | − | 25 100 | ) |
| = | 1 5600 | x | − | 2 105 | × | 1 | + | 2 105 | × | 25 100 |
| = | 1 5600 | x | − | 2 105 | + | 1 210 |
| = | 1 5600 | x | − | 1 70 |
1 5600 | x | − | 1 70 | = | 0 |
1 5600 | x | = | 0 | + | 1 70 |
1 5600 | x | = | 1 70 |
| x | = | 1 70 | ÷ | 1 5600 |
| = | 1 70 | × | 5600 |
| = | 1 | × | 80 |
| x | = | 80 |