I suck this

Thank you so much 

20. Using the Law of Cosines, we have

13^2 = 10^2 + 8^2  - 2(10)(8)cos(K)

5 =   -160 cos (K)     divide by - 160

-1/32  = cos(K)

arccos (-1/32) = K  ≈ 91.8°

21. Using the Law of Sines, we have

sin A / 8  = sin (120)/ 10

sin A  = (8/10)sqrt(3)/2

sinA  = .4sqrt(3)

arcsin(.4sqrt(3))  = A  

So m< C  = 180 - B - A  =  180 - 120 - arcsin(.4sqrt(3)) ≈ 16.1°

have no idea what that guy is talking about