[Math] How many different telephone numbers are possible in city​ A

Question

The local​ seven-digit telephone numbers in city A have $555$ as the first three digits. How many different telephone numbers are possible in city​ A?

Answer 1

There are $10$ possibilities ($0, 1, 2, 3, 4, 5, 6, 7, 8, $ and $9$) for the fourth digit,

$10$ for the fifth digit, $10$ for the sixth digit, and $10$ for the seventh digit -- $10^4$ altogether.