If they won 55 of the games, that means they lost the rest of the 75. So,
75 - 55 = 20 games lost. To find the percentage of 20 out of 75, you set up a proportion:

where x = the percentage of games lost. Cross multiply and divide to isolate the x:

Rounded to the nearest hundredth, the Royals lost 26.667 % of their games.