Answer:
Missing Angle = 75 degrees
This answer may not be correct, if it is or is not, please tell me in the comments!
Explanation:
The Missing Angle:
All of the angles add up to 180 since it is a triangle, so the equation is:
90 (the box aka right angle) + 15 + (the missing angle) = 180
Then, add 90 + 15 = 105. After that, do:
180 - 105 = 75 degrees (don't forget the label!)
I am so sorry, but unfortunately, I do not know the answer for finding the lengths of the sides x and y.