12/15 games have been won then they won 3 which makes it then 15/18 because the denominator is how many games they've played while the numerator is how many games they one.
[tex] \frac{15}{18} = \frac{x}{100} [/tex]
Cross multiply both...
[tex]1500=18x[/tex]
divide each side by 18 to make the x by itself
Which gives you x=83.333%
