Well simply put we know that Celia's collection of cards is bigger because it tells us that it is 4/3 times bigger than franks. If you convert 4/3 to a percent you would see that is is over a hundred percent, so you know hers is bigger than his.
Order of operations is one way
13x - 6y = 22
x - y = 6
6(x-y) = 6*6
6x - 6y = 36
subtract both the equations
13x - 6x -6y + 6y = -14
7x = -14
x = -2
13*-2 -6y=22
-26 -6y=22
-6y = 48
y = -8
answer: x = -2
y = -8
