$\Sigma M_{R2} = 0$
$4R_1 = 200(4)(2) + \frac{1}{2}(3)(400)(1)$
$R_1 = 550 \, \text{N}$
$\Sigma M_{R1} = 0$
$4R_2 = 200(4)(2) + \frac{1}{2}(3)(400)(3)$
$R_2 = 850 \, \text{N}$
$(Area_{AB})\, \bar{X}_A = \frac{1}{2}(4)(2200)(\frac{8}{3}) - \frac{1}{3}(4)(1600)(3) - \frac{1}{4}(3)(600)(\frac{17}{5})$
$(Area_{AB})\, \bar{X}_A = 3 \, 803.33 \, \text{N}\cdot\text{m}^3$ answer
$(Area_{AB})\, \bar{X}_B = \frac{1}{2}(4)(2200)(\frac{4}{3}) - \frac{1}{3}(4)(1600)(1) - \frac{1}{4}(3)(600)(\frac{3}{5})$
$(Area_{AB})\, \bar{X}_B = 3 \, 463.33 \, \text{N}\cdot\text{m}^3$ answer