| ( | 8 | + | 5 | ) | × | 20 | + | ( | 5 | + | x | ) | × | 12 | = | 400 |
| Left side of the equation = | 8 | × | 20 | + | 5 | × | 20 | + | ( | 5 | + | x | ) | × | 12 |
| = | 160 | + | 100 | + | ( | 5 | + | x | ) | × | 12 |
| = | 260 | + | ( | 5 | + | x | ) | × | 12 |
| = | 260 | + | 5 | × | 12 | + | x | × | 12 |
| = | 260 | + | 60 | + | x | × | 12 |
| = | 320 | + | 12 | x |
| 320 | + | 12 | x | = | 400 |
| 12 | x | = | 400 | − | 320 |
| 12 | x | = | 80 |
| x | = | 80 | ÷ | 12 |
| = | 80 | × | 1 12 |
| = | 20 | × | 1 3 |
| x | = | 20 3 |
| x | = | 6.666667 |