| ( | 400 | − | y | ) | ( | 8 | + | 2 25 | y | ) | = | 5000 |
| Left side of the equation = | 400 | ( | 8 | + | 2 25 | y | ) | − | y | ( | 8 | + | 2 25 | y | ) |
| = | 400 | × | 8 | + | 400 | × | 2 25 | y | − | y | ( | 8 | + | 2 25 | y | ) |
| = | 3200 | + | 32 | y | − | y | ( | 8 | + | 2 25 | y | ) |
| = | 3200 | + | 32 | y | − | y | × | 8 | − | y | × | 2 25 | y |
| = | 3200 | + | 24 | y | − | y | × | 2 25 | y |
| 3200 | + | 24 | y | − | y | × | 2 25 | y | = | 5000 |