Answer:
Preston has 19 games and Horatio has 30 games
Explanation:
This problem is solved by a system of equations. First, the variables are defined:
p: Preston video games
h: Horatio video games
It is known that between them they have 49 video games, that is to say that between them they add 49 games. So the first equation is p+h=49.
On the other hand, it is known that Horatio has 11 video games more than Preston. This means that h=p+11
So, now you have the system of equations. To solve it, there are several methods. In this case the substitution is used, which consists on isolate a variable in one of your equations and replacing on the other equation.
In this case, you have an isolated variable: h=p+11. By replacing it in p+h=49, you get: p+p+11=49
Now you have an equation with a variable, which can be solved:
2*p+11=49
2*p=49-11
2*p=38

p=19
This means that Preston has 19 video games.
Now you have to determinate how many video games have Horatio. For that you know that h=p+11, and you knwo the value of p. Simply replacing you get the value of h
h=p+11
h=19+11
h=30
This means that Horatio has 30 video games.