If line ad is a tangent to circle b at point c, and m∠abc = 55º, what is the measure of ∠bad?
135º
100º
145º
155º

The tangent AD at point C forms a right angle to circle B, such as ∠ACB=90° and ∠ABC=55°.

We also know that the summation of all angles in a triangle is 180°. Thus we have the expression below:
180°=∠ABC + ∠ACB + ∠BAD
180°=55°+90°+∠BAD
∠BAD=35°

Therefore, the answer is 35°.