| 49 | + | 1 5 | ( | t | − | 200 | ) | + | 3 10 | × | 40 | = | 69 | + | 3 20 | ( | t | − | 250 | ) |
| 方程左边 = | 49 | + | 1 5 | ( | t | − | 200 | ) | + | 12 |
| = | 61 | + | 1 5 | ( | t | − | 200 | ) |
| 61 | + | 1 5 | ( | t | − | 200 | ) | = | 69 | + | 3 20 | ( | t | − | 250 | ) |
| 方程左边 = | 61 | + | 1 5 | t | − | 1 5 | × | 200 |
| = | 61 | + | 1 5 | t | − | 40 |
| = | 21 | + | 1 5 | t |
| 21 | + | 1 5 | t | = | 69 | + | 3 20 | ( | t | − | 250 | ) |
| 方程右边 = | 69 | + | 3 20 | t | − | 3 20 | × | 250 |
| = | 69 | + | 3 20 | t | − | 75 2 |
| = | 63 2 | + | 3 20 | t |
| 21 | + | 1 5 | t | = | 63 2 | + | 3 20 | t |
1 5 | t | − | 3 20 | t | = | 63 2 | − | 21 |
1 20 | t | = | 63 2 | − | 21 |
1 20 | t | = | 21 2 |
| t | = | 21 2 | ÷ | 1 20 |
| = | 21 2 | × | 20 |
| = | 21 | × | 10 |
| t | = | 210 |