
$\Sigma F_H = 0$
$N_A \cos 15^\circ = N_B \cos 75^\circ$
$N_A = 0.2679N_B$
$\Sigma F_V = 0$
$N_A \sin 15^\circ + N_B \sin 75^\circ = 30$
$(0.2679N_B) \sin 15^\circ + N_B \sin 75^\circ = 30$
$1.0353N_B = 30$
$N_B = 28.98 \, \text{ kN}$
$N_A = 0.2679(28.98)$
$N_A = 7.76 \, \text{ kN}$
$\mu = \tan 15^\circ = 0.2679$
$f_A = \mu N_A = 0.2679(7.76)$
$f_A = 2.08 \, \text{ kN}$
$f_B = \mu N_B = 0.2679(28.98)$
$f_B = 7.76 \, \text{ kN}$
Required couple
$C = \Sigma M_{center}$
$C = 1.5(f_A + f_B) = 1.5(2.08 + 7.76)$
$C = 14.76 \, \text{ kN}\cdot\text{m}$ answer