Point o is the center of this circle. what is mbca? a.) 56° b.) 62° c.) 72° d.) 76°

We are looking for BCA:

OBD = 90   

Reason: Line BD is tangent to circle, and as such it forms a 90 degrees with point of tangency.

Similarly:  OAD = 90  

Reason: Line DA is tangent to circle, and as such it forms a 90 degrees with point of tangency.

So angles in quadrilateral: BOAD

56, 90, 90 and BOA

56 + 90 + 90 + BOA = 360

BOA = 360 - 90 -90 - 56

BOA = 124

Angle BCA is angle at circumference

Angle BOA = 124, is the angle at centre

Angle at Centre = 2* Angle at circumference

Angle at Circumference = Angle at Centre / 2 = 124/2 = 62

Angle BCA = 62 degrees

Option B. 

I hope this helps.