To solve these types of questions, all what you need to do is simply solve for any one of the variables provided above and substitute the solved variable for the other equation. For instance in the first example:
X/2 - 2y = 5
12y + X - 2 = 0
X = 2 - 12y
(2 - 12y)/2 - 2y = 5
(2 - 12y)/2 = 2y + 5
2 - 12y = 2(2y + 5)
2 - 12y = 4y + 10
16 y + 8 = 0
16y = -8
Y =-8/16 = -1/2.
X = 2 - 12(-1/2)
X = 2 + 6
X = 8.
P(X, y) = P(8, -1/2).
Do the same method, for the other questions, except simplify them before doing so.