if linear graph shows 1 marked on y and the second mark is directly on -2x

Question

then the answer is m= -1/2

Answer 1

If you mean the points:
(0,1) and (-2,0)
then the slope is
(0-1)/(-2-0) = -1/-2 = +1/2

Answer 2

If you are actually looking at the graph and it slopes up to the right, then m is positive.