| ( | x | − | 64 | ) | ÷ | 400 | = | ( | x | − | 40 | ) | ÷ | 420 |
| Left side of the equation = | x | × | 1 400 | − | 64 | × | 1 400 |
| = | x | × | 1 400 | − | 4 25 |
1 400 | x | − | 4 25 | = | ( | x | − | 40 | ) | ÷ | 420 |
| Right side of the equation = | x | × | 1 420 | − | 40 | × | 1 420 |
| = | x | × | 1 420 | − | 2 21 |
1 400 | x | − | 4 25 | = | 1 420 | x | − | 2 21 |
1 400 | x | − | 1 420 | x | = | - | 2 21 | + | 4 25 |
1 8400 | x | = | - | 2 21 | + | 4 25 |
1 8400 | x | = | 34 525 |
| x | = | 34 525 | ÷ | 1 8400 |
| = | 34 525 | × | 8400 |
| = | 34 | × | 16 |
| x | = | 544 |