Answer:
Since angle d, a, and e are supplementary, d+a+e =180 degrees.
Given that line LK and BC are parallel
By the alternate interior angle theorem, e=c and d=b.
Substitute:
d+a+e=b+a+c=180
Since b+a+c is the sum of the angles of triangle ABC, the sum of the interior angle of triangle ABC (which could be any triangle of any size and shape) is 180 degrees.
