I'm confused on #21. it's very hard. i tried starting it but i gave up.

Pls , the question is in the picture!

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?

What’s the volume of the triangular prism?