How do i make 1\2x-y=4 into slope intercept form

Simple, since you want to find y, in y=mx+b form, move everything to the other side.

1/2x-y=4

Move 1/2x

1/2x-y=4
-1/2x     -1/2x

Making it look like,

-y=4-1/2x

Divide by the negative 1 in front of the y,

-y=4-1/2x
/-1    /-1

y=-4+1/2x

or 

y=1/2x-4

Thus, this written in y=mx+b form, y=1/2x-4.