| 4 | ( | a | + | a | + | 1 | + | a | + | 2 | ) | × | 3 | = | 288 |
| Left side of the equation = | 12 | ( | a | + | a | + | 1 | + | a | + | 2 | ) |
| 12 | ( | a | + | a | + | 1 | + | a | + | 2 | ) | = | 288 |
| Left side of the equation = | 12 | a | + | 12 | a | + | 12 | × | 1 | + | 12 | a | + | 12 | × | 2 |
| = | 12 | a | + | 12 | a | + | 12 | + | 12 | a | + | 24 |
| = | 36 | a | + | 36 |
| 36 | a | + | 36 | = | 288 |
| 36 | a | = | 288 | − | 36 |
| 36 | a | = | 252 |
| a | = | 252 | ÷ | 36 |
| = | 252 | × | 1 36 |
| = | 7 | × | 1 |
| a | = | 7 |