| x | − | 1 | ÷ | 4 | × | x | − | 16 | − | ( | ( | 1 | ÷ | 4 | × | x | + | 16 | ) | ÷ | 2 | ) | = | 21 |
| Left side of the equation = | x | − | 1 4 | x | − | 16 | − | ( | ( | 1 | ÷ | 4 | × | x | + | 16 | ) | ÷ | 2 | ) |
| = | 3 4 | x | − | 16 | − | ( | ( | 1 | ÷ | 4 | × | x | + | 16 | ) | ÷ | 2 | ) |
3 4 | x | − | 16 | − | ( | ( | 1 | ÷ | 4 | × | x | + | 16 | ) | ÷ | 2 | ) | = | 21 |
| Left side of the equation = | 3 4 | x | − | 16 | − | ( | 1 | ÷ | 4 | × | x | + | 16 | ) | ÷ | 2 |
| = | 3 4 | x | − | 16 | − | 1 | ÷ | 4 | × | x | × | 1 2 | − | 16 | × | 1 2 |
| = | 3 4 | x | − | 16 | − | 1 8 | x | − | 8 |
| = | 5 8 | x | − | 24 |
5 8 | x | − | 24 | = | 21 |
5 8 | x | = | 21 | + | 24 |
5 8 | x | = | 45 |
| x | = | 45 | ÷ | 5 8 |
| = | 45 | × | 8 5 |
| = | 9 | × | 8 |
| x | = | 72 |