To figure out how many cards are in each deck, divide 312 by 6. That comes out to a quotient of 52. That means there are 52 cards in each deck.
#5, the way to figure out which is the better deal, is to multiply the 2 package by the 5 package (note, DO NOT multiply the prices, only how many games they hold) that comes out to 10. So, what you do know is multiply the 2 games price by 5.
$11.98 * 5 = $59.9
Do the same with the 5 package, except multiply it by 2.
$24.95 * 2 = $49.9
Now, with these 2 answers you can tell that the 5 game package is $10 cheaper than the 2 game package, even though you are getting the same amount of games.
Hope this helps a little!