Need help! I think this is pretty easy but I'm missing something

What properties allow transformation to be used as a problem solving tool

Tom had a total of $220 and he spent $35 on a basketball ticket . what percent of his money did he have left?

Hector and alex traded video games. alex gave hector one fourth of his video games in exchange for 6 video games. then he sold 3 video games and gave 2 video games to his brother. alex ended up with 16 video games. how many video games did alex have when he started?