Hey There!!
The answer to this is: (3:1) 36:12. 36 is the teeth on the front socket and 12 is the teeth on the rear socket. All you need to do is simplify by finding the greatest common factor (GCF) of 36 and 12-which is 12, then divide by the GCF. This gives you 3:1. The gear ratio for the bike is 3 teeth on the front socket for every 1 teeth on the rear socket (3:1).
Hope It Helped!~ ♡
ItsNobody~ ☆