| ( | 400 | − | x | − | 240 | ) | ( | 200 | + | 4 | x | ) | = | 41600 |
| Left side of the equation = | 400 | ( | 200 | + | 4 | x | ) | − | x | ( | 200 | + | 4 | x | ) | − | 240 | ( | 200 | + | 4 | x | ) |
| = | 400 | × | 200 | + | 400 | × | 4 | x | − | x | ( | 200 | + | 4 | x | ) | − | 240 | ( | 200 | + | 4 | x | ) |
| = | 80000 | + | 1600 | x | − | x | ( | 200 | + | 4 | x | ) | − | 240 | ( | 200 | + | 4 | x | ) |
| = | 80000 | + | 1600 | x | − | x | × | 200 | − | x | × | 4 | x | − | 240 | ( | 200 | + | 4 | x | ) |
| = | 80000 | + | 1400 | x | − | x | × | 4 | x | − | 240 | ( | 200 | + | 4 | x | ) |
| = | 80000 | + | 1400 | x | − | x | × | 4 | x | − | 240 | × | 200 | − | 240 | × | 4 | x |
| = | 80000 | + | 1400 | x | − | x | × | 4 | x | − | 48000 | − | 960 | x |
| = | 32000 | + | 440 | x | − | x | × | 4 | x |
| 32000 | + | 440 | x | − | x | × | 4 | x | = | 41600 |