| ( | 60 | + | 2 | a | ) | ( | 40 | − | a | ) | + | ( | 40 | + | 3 | a | ) | ( | 35 | − | a | ) | = | 4100 |
| Left side of the equation = | 60 | ( | 40 | − | a | ) | + | 2 | a | ( | 40 | − | a | ) | + | ( | 40 | + | 3 | a | ) | ( | 35 | − | a | ) |
| = | 60 | × | 40 | − | 60 | a | + | 2 | a | ( | 40 | − | a | ) | + | ( | 40 | + | 3 | a | ) | ( | 35 | − | a | ) |
| = | 2400 | − | 60 | a | + | 2 | a | ( | 40 | − | a | ) | + | ( | 40 | + | 3 | a | ) | ( | 35 | − | a | ) |
| = | 2400 | − | 60 | a | + | 2 | a | × | 40 | − | 2 | a | a | + | ( | 40 | + | 3 | a | ) | ( | 35 | − | a | ) |
| = | 2400 | − | 60 | a | + | 80 | a | − | 2 | a | a | + | ( | 40 | + | 3 | a | ) | ( | 35 | − | a | ) |
| = | 2400 | + | 20 | a | − | 2 | a | a | + | ( | 40 | + | 3 | a | ) | ( | 35 | − | a | ) |
| = | 2400 | + | 20 | a | − | 2 | a | a | + | 40 | ( | 35 | − | a | ) | + | 3 | a | ( | 35 | − | a | ) |
| = | 2400 | + | 20 | a | − | 2 | a | a | + | 40 | × | 35 | − | 40 | a | + | 3 | a |
| = | 2400 | + | 20 | a | − | 2 | a | a | + | 1400 | − | 40 | a | + | 3 | a | ( | 35 | − | a | ) |
| = | 3800 | − | 20 | a | − | 2 | a | a | + | 3 | a | ( | 35 | − | a | ) |
| = | 3800 | − | 20 | a | − | 2 | a | a | + | 3 | a | × | 35 | − | 3 | a | a |
| = | 3800 | − | 20 | a | − | 2 | a | a | + | 105 | a | − | 3 | a | a |
| = | 3800 | + | 85 | a | − | 2 | a | a | − | 3 | a | a |
| 3800 | + | 85 | a | − | 2 | a | a | − | 3 | a | a | = | 4100 |