| ( | 58 | − | a | − | 35 | ) | ( | 500 | + | 20 | a | ) | = | 8400 |
| Left side of the equation = | 58 | ( | 500 | + | 20 | a | ) | − | a | ( | 500 | + | 20 | a | ) | − | 35 | ( | 500 | + | 20 | a | ) |
| = | 58 | × | 500 | + | 58 | × | 20 | a | − | a | ( | 500 | + | 20 | a | ) | − | 35 | ( | 500 | + | 20 | a | ) |
| = | 29000 | + | 1160 | a | − | a | ( | 500 | + | 20 | a | ) | − | 35 | ( | 500 | + | 20 | a | ) |
| = | 29000 | + | 1160 | a | − | a | × | 500 | − | a | × | 20 | a | − | 35 | ( | 500 | + | 20 | a | ) |
| = | 29000 | + | 660 | a | − | a | × | 20 | a | − | 35 | ( | 500 | + | 20 | a | ) |
| = | 29000 | + | 660 | a | − | a | × | 20 | a | − | 35 | × | 500 | − | 35 | × | 20 | a |
| = | 29000 | + | 660 | a | − | a | × | 20 | a | − | 17500 | − | 700 | a |
| = | 11500 | − | 40 | a | − | a | × | 20 | a |
| 11500 | − | 40 | a | − | a | × | 20 | a | = | 8400 |