| 39 | ( | 50 | × | 9 10 | − | 35 | ) | + | 21 | ( | 100 | x | ÷ | 10 | − | 65 | ) | = | 810 |
| Left side of the equation = | 39 | × | 50 | × | 9 10 | − | 39 | × | 35 | + | 21 | ( | 100 | x | ÷ | 10 | − | 65 | ) |
| = | 1755 | − | 1365 | + | 21 | ( | 100 | x | ÷ | 10 | − | 65 | ) |
| = | 390 | + | 21 | ( | 100 | x | ÷ | 10 | − | 65 | ) |
| = | 390 | + | 21 | × | 100 | x | ÷ | 10 | − | 21 | × | 65 |
| = | 390 | + | 210 | x | − | 1365 |
| = | - | 975 | + | 210 | x |
| - | 975 | + | 210 | x | = | 810 |
| 210 | x | = | 810 | + | 975 |
| 210 | x | = | 1785 |
| x | = | 1785 | ÷ | 210 |
| = | 1785 | × | 1 210 |
| = | 17 | × | 1 2 |
| x | = | 17 2 |
| x | = | 8.5 |