How many 5-digit telephone numbers can be constructed using the digits 0 to 9 if each number starts with 67 and no digit appears more than once?

Explanation

To solve the problem of how many 5-digit telephone numbers can be constructed using the digits 0 to 9, starting with "67" and ensuring that no digit appears more than once, we can follow these steps:

### Step-by-Step Solution:

1. **Identify Fixed Digits**:
The first two digits of the telephone number are fixed as "67". Therefore, we only need to determine the last three digits of the 5-digit number.

2. **Count Available Digits**:
...