INFO:

B^(2)=B(V)^(2)+B(H)^(2) implies B(V)=sqrt(B^(2)-B(H)^(2))=sqrt((0.5)^(2)-(0.3)^(2))=0.4 Now tan varphi=B(V)/B(H)=0.4/0.3=4/3 implies varphi=tan^(-1)(4/3).