| ( | 5 | + | x | ) | ( | 450 | + | 150 | x | ) | = | 2400 |
| Left side of the equation = | 5 | ( | 450 | + | 150 | x | ) | + | x | ( | 450 | + | 150 | x | ) |
| = | 5 | × | 450 | + | 5 | × | 150 | x | + | x | ( | 450 | + | 150 | x | ) |
| = | 2250 | + | 750 | x | + | x | ( | 450 | + | 150 | x | ) |
| = | 2250 | + | 750 | x | + | x | × | 450 | + | x | × | 150 | x |
| = | 2250 | + | 1200 | x | + | x | × | 150 | x |
| 2250 | + | 1200 | x | + | x | × | 150 | x | = | 2400 |