If you draw a line from the X to the opposite side you get 5 and the long side is the hypotenuse So this is sine opposite over hypotenuse Sin ^-1= 5/14 Answer 20.9 degrees
A proof is basically evidence from theorms, when you said given it doesn't make sense because what evidence is supporting your saying, does it physically say that this number equals this.
Study the theorms that you learned and maybe you'll find it.