| ( | x | − | 70 | ) | ( | 20 | + | 2 | ( | 110 | − | x | ) | ) | = | 1200 |
| Left side of the equation = | x | ( | 20 | + | 2 | ( | 110 | − | x | ) | ) | − | 70 | ( | 20 | + | 2 | ( | 110 | − | x | ) | ) |
| = | x | × | 20 | + | x | × | 2 | ( | 110 | − | x | ) | − | 70 | ( | 20 | + | 2 | ( | 110 | − | x | ) | ) |
| = | 20 | x | + | x | × | 2 | × | 110 | − | x | × | 2 | x | − | 70 | ( | 20 | + | 2 | ( | 110 | − | x | ) | ) |
| = | 20 | x | + | x | × | 220 | − | x | × | 2 | x | − | 70 | ( | 20 | + | 2 | ( | 110 | − | x | ) | ) |
| = | 240 | x | − | x | × | 2 | x | − | 70 | ( | 20 | + | 2 | ( | 110 | − | x | ) | ) |
| = | 240 | x | − | x | × | 2 | x | − | 70 | × | 20 | − | 70 | × | 2 | ( | 110 | − | x | ) |
| = | 240 | x | − | x | × | 2 | x | − | 1400 | − | 140 | ( | 110 | − | x | ) |
| = | 240 | x | − | x | × | 2 | x | − | 1400 | − | 140 | × | 110 | + | 140 | x |
| = | 240 | x | − | x | × | 2 | x | − | 1400 | − | 15400 | + | 140 | x |
| = | 380 | x | − | x | × | 2 | x | − | 16800 |
| 380 | x | − | x | × | 2 | x | − | 16800 | = | 1200 |