so from my original question the first slope =2 so would the second =-1/2?
Yes.
So for the equation of the line you are trying to find, it is of the form y = mx + c, and you have now found m = -1/2, use this and the fact that (x, y) = (0, 0) is a point that lies on the line, to evaluate c.
Andy, please stop posting your "guesses"; wastes everybody's time.
You apparently still can't see that C = 0.
Only a teacher in a classroom can help you.