What is 21x=7 simplify

Valentina is subtracting from . she finds the lcd to be 15y2. what is valentina's next step?

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?

Can someone answer this question for me