| ( | 800 | − | y | ) | ( | 1200 | + | 1 5 | y | ) | = | 854000 |
| Left side of the equation = | 800 | ( | 1200 | + | 1 5 | y | ) | − | y | ( | 1200 | + | 1 5 | y | ) |
| = | 800 | × | 1200 | + | 800 | × | 1 5 | y | − | y | ( | 1200 | + | 1 5 | y | ) |
| = | 960000 | + | 160 | y | − | y | ( | 1200 | + | 1 5 | y | ) |
| = | 960000 | + | 160 | y | − | y | × | 1200 | − | y | × | 1 5 | y |
| = | 960000 | − | 1040 | y | − | y | × | 1 5 | y |
| 960000 | − | 1040 | y | − | y | × | 1 5 | y | = | 854000 |