Question

Given: DR tangent to Circle O.

If m DB = 150°, then A = degrees

click pic below

Answer 1

Not sure why you would need that DR is tangent to Circle O (Geometry was a while ag for me), but since m(arc DB) = 150, m(arc DCB) = 210. Since point A is on the circle, m(angle A) = (1/2)m(arc DCB) = (1/2)(210) = 105.