Answer :

Demon
x-2y = 3

-2y=3-x move the x over to the other side 

-y=3/2 -1/2x divide both sides by 2

y=1/2x - 3/2 divide both sides by -1

Let us solve your problem now,

x - 2y = 3

or, -2y = 3-x

thus, -y = 3/2 - 1/2 x

dividing both sides by -1, we get

y = 1/2x - 3/2