| ( | 1 5 | + | x | ) | ( | 400 | + | x | ÷ | 5 | ) | = | 3 20 |
| Left side of the equation = | 1 5 | ( | 400 | + | x | ÷ | 5 | ) | + | x | ( | 400 | + | x | ÷ | 5 | ) |
| = | 1 5 | × | 400 | + | 1 5 | x | ÷ | 5 | + | x | ( | 400 | + | x | ÷ | 5 | ) |
| = | 80 | + | 1 25 | x | + | x | ( | 400 | + | x | ÷ | 5 | ) |
| = | 80 | + | 1 25 | x | + | x | × | 400 | + | x | x | ÷ | 5 |
| = | 80 | + | 10001 25 | x | + | x | x | × | 1 5 |
| 80 | + | 10001 25 | x | + | x | x | × | 1 5 | = | 3 20 |