Based on how 20 is the angle as you can see by the arrow I made the assumption that a is 20 degrees and for c my estimated guess is 90 because if you imagine how many of the 20 degree angle can fit there you get around 80-90 so I made the guess it was option C. I am sorry if this doesn't make sense I tired to understand it I hope you get the answer right. Also enjoy the rest of your day!
