Please solve question no.14.

Dear student,

In △ABC
∠B=∠C.....(1)
In the cyclic quadrilateral CBDE,
​​​​​side BD is produced to A.
We know that exterior angle is equal to opposite interior angle.
i.e ∠D=∠C....(2)
From (1) and (2)
∠ADE=∠ABC
So, corresponding angles are equal
  Hence, DE∣∣BC
Regards.