Sports outcome probability

#1
Hello! Here is the scenario I have:
In ice hockey, team A is ahead at the end of the 2nd period (they have games of 3 periods for those who do not know). When team A is ahead at this point in the game, they go on to win 75% of the time. When team B is losing at the end of the 2nd period, as they are in this scenario, they go on to win only 10% of the time.

What I want to do is figure out what is the probability of team A winning considering these two numbers.

I'm not sure where to start here, or how hard or simple this would be to figure out. So any help is greatly appreciated. Thank you
 
#2
The first thought I had was if I subtracted the number of team B (10%) from the number of team A (75%) that I would be able to say with 65% certainty that team A would win [75%-10%=65%]. Of course I have no idea if that is valid or not, maybe someone can confirm or deny this?