$\cos \theta = \dfrac{a}{500} = \dfrac{4}{5}$
$a = 400 ~ \text{mm}$
$\sec \theta = \dfrac{b}{400} = \dfrac{5}{4}$
$b = 500 ~ \text{mm}$
$\Sigma M_1 = 0$
$(a + b)R_2 = (500 + 400 + 100)450$
$900R_2 = (1000)450$
$R_2 = 500 ~ \text{kN}$
$\cos \theta = \dfrac{c}{200} = \dfrac{4}{5}$
$c = 160 ~ \text{mm}$
$M_3 = 500(200) - 450(c + 100)$
$M_3 = 100,000 - 450(160 + 100)$
$M_3 = -17,000 ~ \text{kN}\cdot\text{mm}$
$M_3 = 17,000 ~ \text{kN}\cdot\text{mm clockwise}$
$F_a = 450 \sin \theta = 450(3/5)$
$F_a = 270 ~ \text{kN}$
$\sigma_a = \dfrac{P}{A} = \dfrac{270(1000)}{200(200)}$
$\sigma_a = 6.75 ~ \text{MPa}$
$\sigma_f = \dfrac{6M}{bd^2} = \dfrac{6(17,000)(1000)}{200(200^2)}$
$\sigma_f = 12.75 ~ \text{MPa}$
$\sigma_A = -\sigma_a + \sigma_f = -6.75 + 12.75$
$\sigma_A = 6 ~ \text{MPa}$ answer
$\sigma_B = -\sigma_a - \sigma_f = -6.75 + 12.75$
$\sigma_B = -19.5 ~ \text{MPa}$ answer
