A) $ 79{}^\circ $
B) $ 72{}^\circ $
C) $ 74{}^\circ $
D) $ 74{}^\circ $
Correct Answer: B
$ \Rightarrow $ $ 4x+3x+3x=180{}^\circ $
$ \Rightarrow $ $ x=18{}^\circ $
$ AB||CD $ and $ BC $ is the transversal, then
$ \angle ABC+\angle BCD=180{}^\circ $
[sum of the internal angles on the same side of the transversal]
$ \Rightarrow $ $ \angle ABC+\angle BCA+\angle ACD=180{}^\circ $
$ \Rightarrow $ $ 4x+3x+\angle ACD=180{}^\circ $
$ \Rightarrow $ $ \angle ACD=180{}^\circ -7x $
$ \Rightarrow $ $ \angle ACD=180{}^\circ -7\times 18{}^\circ =54{}^\circ $ Also, $ \angle ACE=\angle CAB+\angle ABC $ exterior angle is equal to the sum of interior opposite angles. $ \angle ACD+\angle DCE=3x+4x=7x $
$ \Rightarrow $ $ 54{}^\circ +y=7\times 18{}^\circ =126{}^\circ $
$ \Rightarrow $ $ y=126{}^\circ -54{}^\circ =72{}^\circ $