The first step, would be to make the percent a fraction. 15%=15/100.
So, if they played 60 games, and you want to find how many they lost, you would write x/60, when x=games lost.
15 x
___=___
100 60
Simplify the fraction on the left. Divide the numerator (top) and the denominator (bottom) by 5, leaving you with 3/20.
3/20=x/60
Make the denominators (bottom) similar
9/60=x/60
x=9