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180° - 140° = 40°

 ( y + 10 ) + ( 2y + 10 ) + 40 = 180
y + 2y + 10 + 10 + 40 = 180
3y + 60 = 180
3y = 180 - 60
3y = 120
y = 120/3
y = 40

BAC = ( y + 10 )°
= ( 40 + 10 ) = 50° ( C )