( | 12 | − | y | ) | ( | 300 | + | 50 | y | ) | = | 4000 |
Left side of the equation = | 12 | ( | 300 | + | 50 | y | ) | − | y | ( | 300 | + | 50 | y | ) |
= | 12 | × | 300 | + | 12 | × | 50 | y | − | y | ( | 300 | + | 50 | y | ) |
= | 3600 | + | 600 | y | − | y | ( | 300 | + | 50 | y | ) |
= | 3600 | + | 600 | y | − | y | × | 300 | − | y | × | 50 | y |
= | 3600 | + | 300 | y | − | y | × | 50 | y |
3600 | + | 300 | y | − | y | × | 50 | y | = | 4000 |