North team score is n, south team score is s.
first game equation:
n = (2/3)s
second game equation:
s - 7 = n + 7 - 3
So we have 2 equations and 2 unknowns to solve:
n = (2/3)s
s - 7 = n + 7 - 3
lets substitute the first into the second:
s -7 = (2/3)s + 7 - 3
multiply all equation by 3 to eliminate fraction:
3s - 21 = 2s + 21 - 9
s = 21 + 21 - 9
s = 32
that is the souths score of the first game, now substitute in the first equation:
n = (2/3)s
n = (2/3)(32)
n = 64/3
n = 21
that is the score of the norths in the first game.
For the second game the norths increased the score by seven that is 21 + 7 = 28
While the souths decreased the score by 7, 32 - 7 = 25