Answer:
Option C is correct
The value of y is, 
Step-by-step explanation:
Exterior Angle theorem states that the sum of the measures of the two non-adjacent interior angles of the triangle is equal to the measure of an exterior angle.
Label the figure:
In triangle ABC, BC is produced to D, then
is the exterior angle ,
and
are the two interior opposite angle.
i.e, 
From the given figure:
and 

Then, by the Exterior angle theorem, we calculate the value of y;

Combine like terms:
on simplify:

therefore, the value of y is, 