| ( | 40 | − | y | − | 25 | ) | ( | 400 | + | 5 | y | ) | = | 4250 |
| Left side of the equation = | 40 | ( | 400 | + | 5 | y | ) | − | y | ( | 400 | + | 5 | y | ) | − | 25 | ( | 400 | + | 5 | y | ) |
| = | 40 | × | 400 | + | 40 | × | 5 | y | − | y | ( | 400 | + | 5 | y | ) | − | 25 | ( | 400 | + | 5 | y | ) |
| = | 16000 | + | 200 | y | − | y | ( | 400 | + | 5 | y | ) | − | 25 | ( | 400 | + | 5 | y | ) |
| = | 16000 | + | 200 | y | − | y | × | 400 | − | y | × | 5 | y | − | 25 | ( | 400 | + | 5 | y | ) |
| = | 16000 | − | 200 | y | − | y | × | 5 | y | − | 25 | ( | 400 | + | 5 | y | ) |
| = | 16000 | − | 200 | y | − | y | × | 5 | y | − | 25 | × | 400 | − | 25 | × | 5 | y |
| = | 16000 | − | 200 | y | − | y | × | 5 | y | − | 10000 | − | 125 | y |
| = | 6000 | − | 325 | y | − | y | × | 5 | y |
| 6000 | − | 325 | y | − | y | × | 5 | y | = | 4250 |