7 2 | ( | 400 | − | x | ) | + | 420 | + | 16 5 | × | 80 | + | 3 | ( | x | − | 300 | ) | = | 1336 |
| Left side of the equation = | 7 2 | ( | 400 | − | x | ) | + | 420 | + | 256 | + | 3 | ( | x | − | 300 | ) |
| = | 7 2 | ( | 400 | − | x | ) | + | 676 | + | 3 | ( | x | − | 300 | ) |
7 2 | ( | 400 | − | x | ) | + | 676 | + | 3 | ( | x | − | 300 | ) | = | 1336 |
| Left side of the equation = | 7 2 | × | 400 | − | 7 2 | x | + | 676 | + | 3 | ( | x | − | 300 | ) |
| = | 1400 | − | 7 2 | x | + | 676 | + | 3 | ( | x | − | 300 | ) |
| = | 2076 | − | 7 2 | x | + | 3 | ( | x | − | 300 | ) |
| = | 2076 | − | 7 2 | x | + | 3 | x | − | 3 | × | 300 |
| = | 2076 | − | 7 2 | x | + | 3 | x | − | 900 |
| = | 1176 | − | 1 2 | x |
| 1176 | − | 1 2 | x | = | 1336 |
| - | 1 2 | x | = | 1336 | − | 1176 |
| - | 1 2 | x | = | 160 |
| - | 160 | = | 1 2 | x |
1 2 | x | = | - | 160 |
| x | = | - | 160 | ÷ | 1 2 |
| = | - | 160 | × | 2 |
| x | = | - | 320 |