If two lines are parallel with a common line then these two lines will also be parallel to each other.
If AB ∥ CD and EF ∥ CD then AB ∥ EF.
Find x and y.
A + B + C = 180° (Angle sum property)
30° + 42° + x = 180°
x = 180°- (30° + 42°)
x = 108°
And y is the exterior angle and the two opposite angles are A and B.
BCD = A + B (Exterior angle is equal to the sum of the two interior opposite angles).
y = 30° + 42°
y = 72°