Two chords AB and CD of a circle meet when produced outside the circle at P.
AD and BC are joined.If |_ PAD =30 and |_ CPA is 45, then |_ CBP will be
Notice that because the both subtend from the same arc BD.
Now, if you look at as a triangle, you'll see that you have 2 of the 3 angles. The missing angle is what you're looking for and can be easily found since you know that the angles must add up to 180 degrees.