| 2 | ( | 120 | × | 7 2 | ) | + | 16 5 | ( | 400 | − | x | − | 120 | ) | = | 1336 |
| Left side of the equation = | 2 | × | 120 | × | 7 2 | + | 16 5 | ( | 400 | − | x | − | 120 | ) |
| = | 840 | + | 16 5 | ( | 400 | − | x | − | 120 | ) |
| = | 840 | + | 16 5 | × | 400 | − | 16 5 | x | − | 16 5 | × | 120 |
| = | 840 | + | 1280 | − | 16 5 | x | − | 384 |
| = | 1736 | − | 16 5 | x |
| 1736 | − | 16 5 | x | = | 1336 |
| - | 16 5 | x | = | 1336 | − | 1736 |
| - | 16 5 | x | = | - | 400 |
| 400 | = | 16 5 | x |
16 5 | x | = | 400 |
| x | = | 400 | ÷ | 16 5 |
| = | 400 | × | 5 16 |
| = | 25 | × | 5 |
| x | = | 125 |