First we look for the slope of the line. We know it is parallel to 4x-2y=6. Putting this into slope-intercept form, we get: y=-2x-3. From this we know the slope of the line is -2.
We then find the y-intercept, by plugging in 1 for x and 2 for y in y=-2x+b, and get that 2=-2+b. We now solve for b, which is 4