Section through M-M and N-N

Free Body Diagram to the Left of M-M

$\Sigma M_G = 0$

$6\left( \frac{5}{\sqrt{29}}F_{DF} \right) = 15(200) + 10(200) + 5(400)$

$\frac{30}{\sqrt{29}}F_{DF} = 7000$

$F_{DF} = \frac{700}{3}\sqrt{29} ~ \text{kN} = 1256.54 ~ \text{kN tension}$ *answer*

$\Sigma M_F = 0$

$6F_{GI} = 15(200) + 10(200) + 5(400)$

$6_{FGI} = 7000$

$F_{GI} = \frac{3500}{3} ~ \text{kN} = 1166.67 ~ \text{kN compression}$ *answer*

$\Sigma F_V = 0$

$F_{FG} + \frac{2}{\sqrt{29}}F_{DF} = 200 + 200 + 400 + 400$

$F_{FG} + \frac{2}{\sqrt{29}}\left( \frac{700}{3}\sqrt{29} \right) = 1200$

$F_{FG} = \frac{2200}{3} ~ \text{kN} = 733.33 ~ \text{kN tension}$

Free Body Diagram to the Left of N-N

$\Sigma M_I = 0$

$10\left( \frac{5}{\sqrt{41}}F_{FH} \right) = 20(200) + 15(200) + 10(400) + 5(400)$

$\frac{50}{\sqrt{41}}F_{FH} = 13,000$

$F_{FH} = 260\sqrt{41} ~ \text{kN} = 1664.81 ~ \text{kN tension}$ *answer*

$\Sigma F_V = 0$

$\frac{6}{\sqrt{61}}F_{FI} + \frac{4}{\sqrt{41}}F_{FH} = 200 + 200 + 400 + 400$

$\frac{6}{\sqrt{61}}F_{FI} + \frac{4}{\sqrt{41}}\left( 260\sqrt{41} \right) = 1200$

$\frac{6}{\sqrt{61}}F_{FI} = 160$

$F_{FI} = \frac{80}{3}\sqrt{61} ~ \text{kN} = 208.27 ~ \text{kN compression}$ *answer*