Hey there,
Ok so we need to put this into slope-intercept form so we can find the slope eaisly, (y=mx+b)
If we move x to the right side we are left with,
2y=-x-3
Next we divide by 2 to free up the y,
y=-1/2x-3/2, this is now in y=mx+b form. Making the slope -1/2
Hope this helped!