Hello, thank you for taking the time to post your question!
The key on this type of question is to set up a system of equations based on the information given! If you use “W” to represent the number of wins and “L” to represent the number of losses, for this one that would mean
W + L = 91
W = 3L + 15
From there then you can solve algebraically for the values! I would plug in W = 3L + 15 into the first equation
3L + 15 + L = 91
4L = 76
L = 19, so the team lost 19 games
W = 3(19) + 15 = 57 + 15 = 72, so the team won 72 games
I hope that helps get you moving in the right direction! Feel free to reach out if you have any additional questions beyond that :)