It is given that AB||CD and CD||EF.
Then. AB||CD||EF.
⇒AB||EF (Lines parallel to the same line are parallel to each other)
It can be observed that,
x=z (Alternate interior angles)……(1)
It is given that y:z=3:7
Let the common ratio between y and z be a.
3a+7a=180∘
10a=180∘
a=180∘10
a=18∘
∴x=z=7a=7×18∘=126∘