If you are referring to simultaneous equations (which I think you are), you make the two equations equal to each other.
Since, y is equal to 3/2x and y is also equal to -1/2x + 4,
3/2x must be equal to -1/2x + 4
=> 3/2x=-1/2x + 4
=> 3/2x + 1/2x = 4
=> 4/2x= 4
=> 2x= 4
=> x=2
If x= 2, you can substitute this value in either of the two initial equations to find the value for y :-
y=3/2x
=> y=3/2*( 2)
=> y=3
So your two values for x and y are 2,3
