| ( | 14 5 | − | a | ) | ( | 500 | + | 400 | a | ) | = | 1640 |
| Left side of the equation = | 14 5 | ( | 500 | + | 400 | a | ) | − | a | ( | 500 | + | 400 | a | ) |
| = | 14 5 | × | 500 | + | 14 5 | × | 400 | a | − | a | ( | 500 | + | 400 | a | ) |
| = | 1400 | + | 1120 | a | − | a | ( | 500 | + | 400 | a | ) |
| = | 1400 | + | 1120 | a | − | a | × | 500 | − | a | × | 400 | a |
| = | 1400 | + | 620 | a | − | a | × | 400 | a |
| 1400 | + | 620 | a | − | a | × | 400 | a | = | 1640 |