When you don’t know the degree of a shape just use this form
180(n-2). Where n is the number sides of the shape.
There are 4 sides
180(4-2) = 180(2) = 360
So this shape is 360 degrees
120 + 120 + 60 +x = 360
300 + x = 360
X= 60
But as you can see that you don’t need this form for this question the alternate interior show you that the missing angles is 60