Set up this equation (because the angles in a triangle add up to 180° and because the vertical angles at C are equal):
180 – ( 85 + x) = 180 – ( 110 + y)
180 – 85 – x = 180 – 110 – y
-85 – x (+ 85)= -110 – y ( +85)
- x = - 25 – y
x = y + 25
D
 

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