| 20 | ( | x | − | 200 | × | 3 50 | ) | × | 3 4 | = | 25 | ( | x | − | 200 | × | 3 50 | − | 200 | × | 1 10 | ) | × | 3 4 |
| Left side of the equation = | 15 | ( | x | − | 200 | × | 3 50 | ) |
| 15 | ( | x | − | 200 | × | 3 50 | ) | = | 25 | ( | x | − | 200 | × | 3 50 | − | 200 | × | 1 10 | ) | × | 3 4 |
| Left side of the equation = | 15 | x | − | 15 | × | 200 | × | 3 50 |
| = | 15 | x | − | 180 |
| 15 | x | − | 180 | = | 25 | ( | x | − | 200 | × | 3 50 | − | 200 | × | 1 10 | ) | × | 3 4 |
| Right side of the equation = | 75 4 | ( | x | − | 200 | × | 3 50 | − | 200 | × | 1 10 | ) |
| 15 | x | − | 180 | = | 75 4 | ( | x | − | 200 | × | 3 50 | − | 200 | × | 1 10 | ) |
| Right side of the equation = | 75 4 | x | − | 75 4 | × | 200 | × | 3 50 | − | 75 4 | × | 200 | × | 1 10 |
| = | 75 4 | x | − | 225 | − | 375 |
| = | 75 4 | x | − | 600 |
| 15 | x | − | 180 | = | 75 4 | x | − | 600 |
| 15 | x | − | 75 4 | x | = | - | 600 | + | 180 |
| - | 15 4 | x | = | - | 600 | + | 180 |
| - | 15 4 | x | = | - | 420 |
| 420 | = | 15 4 | x |
15 4 | x | = | 420 |
| x | = | 420 | ÷ | 15 4 |
| = | 420 | × | 4 15 |
| = | 28 | × | 4 |
| x | = | 112 |