| ( | 80 | − | 2 | x | ) | ( | 1200 | + | 200 | x | ) | = | 186000 | + | 1600 | x |
| Left side of the equation = | 80 | ( | 1200 | + | 200 | x | ) | − | 2 | x | ( | 1200 | + | 200 | x | ) |
| = | 80 | × | 1200 | + | 80 | × | 200 | x | − | 2 | x | ( | 1200 | + | 200 | x | ) |
| = | 96000 | + | 16000 | x | − | 2 | x | ( | 1200 | + | 200 | x | ) |
| = | 96000 | + | 16000 | x | − | 2 | x | × | 1200 | − | 2 | x | × | 200 | x |
| = | 96000 | + | 16000 | x | − | 2400 | x | − | 400 | x | x |
| = | 96000 | + | 13600 | x | − | 400 | x | x |
| 96000 | + | 13600 | x | − | 400 | x | x | = | 186000 | + | 1600 | x |