X=60
Explanation:
Since it's a parallelogram, we know the interior angles add up to 360 and that <A =<C as well as angle <B=<D and since x=<D we know that <B=x and that since a=<C that <A=a
So the equation that we would use to define the angles of the parallelogram is
2x+2a=360
Since we know that a=120 we can restructure the equation as
2x+2(120)=360
Or
2x+240=360
If we subtract 240 we get
2x=120
If we divide by 2 to get x alone, we would get
x=60