$\delta_{al} = \delta_{st} + ( \delta_{br} + 0.8)$
$\left( \dfrac{PL}{AE} \right)_{al} = \left( \dfrac{PL}{AE} \right)_{st} + \left( \dfrac{PL}{AE} \right)_{br} + 0.8$
$\dfrac{R_1 \, (500)}{900(70\,000)} = \dfrac{(150\,000 - R_1 )(250)}{2000(200\,000)} + \dfrac{(240\,000 - R_1 )(350)}{1200(83\,000)} + 0.8$
$\dfrac{R_1}{126\,000} = \dfrac{150\,000 - R_1}{1\,600\,000} + \dfrac{7(240\,000 - R_1)}{1\,992\,000} + 0.8$
$\frac{1}{63}R_1 = \frac{1}{800}(150\,000 - R_1) + \frac{7}{996}(240\,000 - R_1) + 1600$
$( \frac{1}{63} + \frac{1}{800} + \frac{7}{996} ) R_1 = \frac{1}{800}(150\,000) + \frac{7}{996}(240\,000) + 1600$
$R_1 = 143\,854 \, \text{ N } = 143.854 \, \text{ kN }$
$P_{al} = R_1 = 143.854 \, \text{kN}$
$P_{st} = 150 - R_1 = 150 - 143.854 = 6.146 \, \text{kN}$
$P_{br} = R_2 = 240 - R_1 = 240 - 143.854 = 96.146 \, \text{kN}$
$\sigma = P/A$
$\sigma_{al} = 143.854(1000)/900$
$\sigma_{al} = 159.84 \, \text{MPa} \, \to \,$ answer
$\sigma_{st} = 6.146(1000)/2000$
$\sigma_{st} = 3.073 \, \text{ MPa}$ answer
$\sigma_{br} = 96.146(1000)/1200$
$\sigma_{br} = 80.122 \, \text{ MPa}}$ answer
