Recall the binomial theorem.

1. The binomial expansion of
is

Observe that


When we multiply these by
,
•
and
combine to make 
•
and
combine to make 
and the sum of these terms is

2. The binomial expansion is

We get the
term when
:

M ∠ BOA = 360° - 250° = 110°
The sum of all interior angles of the quadrilateral AOBC is 360°
m ∠ BCA = 360° - ( 110° + 90° + 90° ) = 360° - 290° = 70°
Answer: C ) 70°