Answer: 5 used video games
First create a system of inequalities:
Let x=used video games
Let y=new video games
4x+2y=84
6x+y=78
now you would solve for x and y which $9 each for used video games and $24 each for new video games.
Now create and equation for Janet to find out how many used videos she can buy after knowing that she had already bought 3 new video games.
Janet's equation:
Let g=number of used video games.
gx+3y=120
Plug into the equation the solution set for x and y
g(9)+3(24)=120
Now solve for g:
g(9)+72=120
g(9)=48
g=5.33333333333333
Since she cant buy 1/3 it would round to 5.