Let x represent the amount of games the won
Let y represent the amount of games they lost
x+y=20 (# games won + #games lost = 20 (since they played 20 games))
x=y+4 (# games won = # games lost + 4)
Substituting the second equation into the first equation,
y+4+y=20
2y+4=20
2y=16
y=8
Substituting the y value into the first equation
x+8=20
x=12.
Therefore they won 12 games.
