From the knot where 400-lb load is hanging
$\Sigma F_H = 0$
$D \sin 75^\circ = C \sin 30^\circ$
$D = 0.5176C$
$\Sigma F_V = 0$
$D \cos 75^\circ + C \cos 30^\circ = 400$
$(0.5176C) \cos 75^\circ + C \cos 30^\circ = 400$
$C = 400 \, \text{ lb}$ answer
$D = 0.5176(400)$
$D = 207.06 \, \text{ lb}$ answer
From the knot where 300-lb load is hanging
$\Sigma F_V = 0$
$B \sin 45^\circ = 300 + C \cos 30^\circ$
$B \sin 45^\circ = 300 + 400 \cos 30^\circ$
$B = 914.16 \, \text{ lb}$ answer
$\Sigma F_H = 0$
$A = B \cos 45^\circ + C \sin 30^\circ$
$A = 914.16 \cos 45^\circ + 400 \sin 30^\circ$
$A = 846.41 \, \text{ lb}$ answer