| ( | X | − | 50 | ) | X | × | 3 | + | ( | X | − | 50 | + | X | ) | X | × | 6 | = | 2100 |
| Left side of the equation = | X | X | × | 3 | − | 50 | X | × | 3 | + | ( | X | − | 50 | + | X | ) | X | × | 6 |
| = | X | X | × | 3 | − | 150 | X | + | ( | X | − | 50 | + | X | ) | X | × | 6 |
| = | X | X | × | 3 | − | 150 | X | + | X | X | × | 6 | − | 50 | X | × | 6 | + | X |
| = | X | X | × | 3 | − | 150 | X | + | X | X | × | 6 | − | 300 | X | + | X | X |
| = | X | X | × | 3 | − | 450 | X | + | X | X | × | 6 | + | X | X | × | 6 |
| X | X | × | 3 | − | 450 | X | + | X | X | × | 6 | + | X | X | × | 6 | = | 2100 |