Alright, lets get started.
Zach has 3/4 hour to play video games.
Lets converts it into minutes.
means
minutes.
It takes him 1/12 hour to set up the system means he has
minutes to set up the system.
So, he has left time for playing =
minutes
Each round of his favorite game takes 1/6 hour means
minutes for each round.
It means he has 40 minutes for playing and each round takes 10 minutes.
So, number of rounds he can play=

He can play 4 rounds of his favorite game. : Answer
Hope it will help :)