I say it is a red marble because as you said, there are 10 red marbles and 6 blue ones and since there are 4 more red marbles, there is a higher perchentage of it being a red marble . (I hope i answered your question)
I think it is C. 60. You can eliminate A because it is not a right angle, and D because the angle is bigger than the given angle. So it is between 50 and 60, and I hope this is right and the picture makes sense