3costheta -4sintheta= 2costheta +sintheta find tan theta

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?

Which coefficient matrix represents a system of linear equations that has a unique solution ? options in photo*

Can someone explain to me how to do