Answer:
So we already knew all three sides, there are more than one way to do it, for example:
sin∠F = HG/HF = 12/13
cos∠F = GF/HF = 5/13
tan∠F = HG/GF = 12/5
ctg∠F = GF/HG = 5/12
All of them will give you the result which is approximately 67°.
