12 5 | ( | 1 | + | a | ) | × | 400 | + | 500 | ( | 1 | + | 2 | a | ) | × | 12 5 | ( | 1 | + | a | ) | = | 21600 | ( | 1 | + | 9 | ÷ | 20 | × | a | ) |
| Left side of the equation = | 960 | ( | 1 | + | a | ) | + | 1200 | ( | 1 | + | 2 | a | ) | ( | 1 | + | a | ) |
| 960 | ( | 1 | + | a | ) | + | 1200 | ( | 1 | + | 2 | a | ) | ( | 1 | + | a | ) | = | 21600 | ( | 1 | + | 9 | ÷ | 20 | × | a | ) |
| Left side of the equation = | 960 | × | 1 | + | 960 | a | + | 1200 | ( | 1 | + | 2 | a | ) | ( | 1 | + | a | ) |
| = | 960 | + | 960 | a | + | 1200 | ( | 1 | + | 2 | a | ) | ( | 1 | + | a | ) |
| = | 960 | + | 960 | a | + | 1200 | × | 1 | ( | 1 | + | a | ) | + | 1200 | × | 2 | a | ( | 1 | + | a | ) |
| = | 960 | + | 960 | a | + | 1200 | ( | 1 | + | a | ) | + | 2400 | a | ( | 1 | + | a | ) |
| = | 960 | + | 960 | a | + | 1200 | × | 1 | + | 1200 | a | + | 2400 | a | ( | 1 | + | a | ) |
| = | 960 | + | 960 | a | + | 1200 | + | 1200 | a | + | 2400 | a | ( | 1 | + | a | ) |
| = | 2160 | + | 2160 | a | + | 2400 | a | ( | 1 | + | a | ) |
| = | 2160 | + | 2160 | a | + | 2400 | a | × | 1 | + | 2400 | a | a |
| = | 2160 | + | 2160 | a | + | 2400 | a | + | 2400 | a | a |
| = | 2160 | + | 4560 | a | + | 2400 | a | a |
| 2160 | + | 4560 | a | + | 2400 | a | a | = | 21600 | ( | 1 | + | 9 | ÷ | 20 | × | a | ) |
| Right side of the equation = | 21600 | × | 1 | + | 21600 | × | 9 | ÷ | 20 | × | a |
| = | 21600 | + | 9720 | a |
| 2160 | + | 4560 | a | + | 2400 | a | a | = | 21600 | + | 9720 | a |