Booker has 85 video games .he has 3 shelves to put them on .each shelf can hold 40 games. how many more games can fit in the shelves.

So you know that Booker has 85 video games and that he has 3 shelves to put each of them on. And you also know that each shelf can hold 40 games. 
So if you multiply 40 games by 3 shelves to find the total number of games that he can put on all the shelves, you will get 120 games.
You know that Booker has 85 video games, and you can fit 120 video games on all the shelves.
To find how many more games Booker can fit in the shelves, you subtract 120 by 85, and you will get 35 video games.
So, Booker can fit 35 more video games in the shelves.

I hope this helps :)