For the larger triangle, by sin rule, sinB/10=sin45/8.2
sinB=10*sin45/8.2
For the small triangle on the left hand side, by sin rule, sinB'/10=sin45/8.2
sinB'=10*sin45/8.2
So sinB=sinB' but as B'>90, B and B' are supplementary
B=sin^-1(10*sin45/8.2)=sin^-1(0.8623)=59.58
B'=180-B=180-59.58=120.42
So the anwser is C
