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This problem trains for: SAT-I, AMC-8, GMAT.

In terms of and , what is the measure of the angle ?

figure

This is a simple angle-chasing situation.

Focus on the angle that is the easiest to find.

figure

In triangle BCD, use the fact that the angles of a triangle add up to 180°.

equation

Use the same fact in triangle ABC:

equation

and substitute the value for y:

equation

equation

equation