When the length of sides are given, you can use law of cosine to find the angles Refer to this website for details https://www.mathsisfun.com/algebra/trig-cosine-law.html
11^=8^2+5^2-2*8*5cosA -80cosA=32 cosA=-0.4 A is about 114 degree use the same method to find out B and C, you will get 42 and 25