1/2x-1/4y=7/2

3/4x+1/3y=19/2

How do i change these into y=?

First thing I would do is get rid of my fractions by multiplying each term by the LCD

so multiply by 4
1/2x-1/4y=7/2
2x - y = 14
Take all terms except the y term to the right side
-y = -2x + 14
divide by -1
y = 2x - 14

repeat the same steps for your second equation and let me know what you got.