| ( | X | − | 40 | ) | ( | 740 | − | 10 | X | ) | = | 2250 |
| Left side of the equation = | X | ( | 740 | − | 10 | X | ) | − | 40 | ( | 740 | − | 10 | X | ) |
| = | X | × | 740 | − | X | × | 10 | X | − | 40 | ( | 740 | − | 10 | X | ) |
| = | 740 | X | − | X | × | 10 | X | − | 40 | × | 740 | + | 40 | × | 10 | X |
| = | 740 | X | − | X | × | 10 | X | − | 29600 | + | 400 | X |
| = | 1140 | X | − | X | × | 10 | X | − | 29600 |
| 1140 | X | − | X | × | 10 | X | − | 29600 | = | 2250 |