\begin{align} ΣF_y=0 =&\cssId{Step1}{F_{Ay} + F_{By} + F_{Cy}=0}\\[3px] &\cssId{Step2}{0 + F_B * sin(α) + F_{Cy}=0}\\[3px] &\cssId{Step3}{F_{Cy}= -F_B * sin(α)}\\[3px] \end{align}
  1. In the first step we make the summation of forces in the y-axis
  2. In the second step we express FBy as FB multiplying the sinus of the angle (doing trigonometry)
  3. In the third step we isolate FCy to one side of the equation and everything else to the other side so that you can solve the equation