| ( | 40 | − | a | ) | ( | 16 | + | 4 | a | ÷ | 5 | ) | = | 720 |
| Left side of the equation = | 40 | ( | 16 | + | 4 | a | ÷ | 5 | ) | − | a | ( | 16 | + | 4 | a | ÷ | 5 | ) |
| = | 40 | × | 16 | + | 40 | × | 4 | a | ÷ | 5 | − | a | ( | 16 | + | 4 | a | ÷ | 5 | ) |
| = | 640 | + | 32 | a | − | a | ( | 16 | + | 4 | a | ÷ | 5 | ) |
| = | 640 | + | 32 | a | − | a | × | 16 | − | a | × | 4 | a | ÷ | 5 |
| = | 640 | + | 32 | a | − | a | × | 16 | − | a | × | 4 5 | a |
| = | 640 | + | 16 | a | − | a | × | 4 5 | a |
| 640 | + | 16 | a | − | a | × | 4 5 | a | = | 720 |