| ( | x | − | 11 | ) | ( | 510 | + | 10 | x | − | 200 | ) | = | 7900 |
| Left side of the equation = | x | ( | 510 | + | 10 | x | − | 200 | ) | − | 11 | ( | 510 | + | 10 | x | − | 200 | ) |
| = | x | × | 510 | + | x | × | 10 | x | − | x | × | 200 | − | 11 | ( | 510 | + | 10 | x | − | 200 | ) |
| = | 310 | x | + | x | × | 10 | x | − | 11 | ( | 510 | + | 10 | x | − | 200 | ) |
| = | 310 | x | + | x | × | 10 | x | − | 11 | × | 510 | − | 11 | × | 10 | x | + | 11 | × | 200 |
| = | 310 | x | + | x | × | 10 | x | − | 5610 | − | 110 | x | + | 2200 |
| = | 200 | x | + | x | × | 10 | x | − | 3410 |
| 200 | x | + | x | × | 10 | x | − | 3410 | = | 7900 |