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?

Number of 5 digit telephone numbers beginning with 67, with no digit repeated is equivalent to filling 67 - - - with digits.
0, 1, 2, 3, 4, 5, 8, 9, i.e. 8 digits = 8 ×7 × 6 = 56 × 6 = 336 ways.