Billy brought 3 video games.
$150 gift card
$35 each video game
$45 balance
$150-$45=$105
$105÷$35(which is how much each video game cost) which equals 3 video game.
When you times the 3 with 35 it equals 105.
So, when you subtract 150 with 105 it equals 45(the balance)
(I'm not good at explaining, sorry if can't understand)