Equating vertical angles
in the figure yields y = 2x + 30. Also, equating vertical angles
yields 5y/2 = 5x + 5a. Multiplying this equation by 2/5 yields y = 2x + 2a. Subtracting
this equation from the equation y = 2x + 30 yields 2a = 30. Hence, a = 30/2 = 15, and the answer is (A).