Answer:
175760000 possible reservation codes
Step-by-step explanation:
Repetition of numerals or letters is permitted in the context of the question.
There are ten options for each digit (even a leading zero is considered a reservation number), and 26 options for each letter (normally upper and lower cases are considered identical). So,
Possible reservations = 10*10*10*10*26*26*26
=10^4*26^3
=175760000
