| ( | 35 | + | 2 5 | x | ) | ( | 20 | + | x | ) | = | 1600 |
| Left side of the equation = | 35 | ( | 20 | + | x | ) | + | 2 5 | x | ( | 20 | + | x | ) |
| = | 35 | × | 20 | + | 35 | x | + | 2 5 | x | ( | 20 | + | x | ) |
| = | 700 | + | 35 | x | + | 2 5 | x | ( | 20 | + | x | ) |
| = | 700 | + | 35 | x | + | 2 5 | x | × | 20 | + | 2 5 | x | x |
| = | 700 | + | 35 | x | + | 8 | x | + | 2 5 | x | x |
| = | 700 | + | 43 | x | + | 2 5 | x | x |
| 700 | + | 43 | x | + | 2 5 | x | x | = | 1600 |