Answer
$\begin{aligned} & F_{A B}=441 \mathrm{~N} \\ & F_{A C}=515 \mathrm{~N} \\ & F_{A D}=221 \mathrm{~N}\end{aligned}$
Work Step by Step
$\begin{aligned} & \mathbf{u}_{A B}=\left\{\frac{3}{5} \mathbf{i}+\frac{4}{5} \mathbf{j}\right\} \\ & \mathbf{u}_{A C}=\left\{-\frac{6}{7} \mathbf{i}-\frac{3}{7} \mathbf{j}+\frac{2}{7} \mathbf{k}\right\} \\ & \mathbf{u}_{A D}=\left\{\frac{4}{5} \mathbf{i}-\frac{3}{5} \mathbf{j}\right\} \\ & \Sigma F_x=0 ; \quad \frac{3}{5} F_{A B}-\frac{6}{7} F_{A C}+\frac{4}{5} F_{A D}=0 \\ & \Sigma F_y=0 ; \quad \frac{4}{5} F_{A B}-\frac{3}{7} F_{A C}-\frac{3}{5} F_{A D}=0 \quad \frac{2}{7} F_{A C}-15(9.81)=0 \\ & \Sigma F_z=0 ; F_{A B}=441 \mathrm{~N} \\ & F_{A C}=515 \mathrm{~N} \\ & F_{A D}=221 \mathrm{~N}\end{aligned}$
