What is the root squar of 100

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?

Someone me! if you’re smart you can solve this!

State one method by which you can recognize a perfect square trinomial.