Answer
$$
\mathbf{M}_{R O}=\{0.650 \mathbf{i}+19.75 \mathbf{j}-9.05 \mathbf{k}\} \mathrm{kN} \cdot \mathrm{m}
$$
Work Step by Step
$$
\begin{aligned}
\mathbf{F}_R= & \mathbf{F}_1+\mathbf{F}_2=\{-1 \mathbf{i}-2 \mathbf{j}-5 \mathbf{k}\} \mathrm{kN} \\
\mathbf{M}_{R O} & =\mathbf{r}_1 \times \mathbf{F}_1+\mathbf{r}_2 \times \mathbf{F}_2 \\
& =\left|\begin{array}{ccc}
\mathbf{i} & \mathbf{j} & \mathbf{k} \\
4 & -0.15 & 0.25 \\
-4 & 2 & -3
\end{array}\right|+\left|\begin{array}{ccc}
\mathbf{i} & \mathbf{j} & \mathbf{k} \\
4 & 0.15 & 0.25 \\
3 & -4 & -2
\end{array}\right| \\
& =(-0.05 \mathbf{i}+11 \mathbf{j}+7.4 \mathbf{k})+(0.7 \mathbf{i}+8.75 \mathbf{j}-16.45 \mathbf{k}) \\
& =(0.65 \mathbf{i}+19.75 \mathbf{j}-9.05 \mathbf{k}) \\
\mathbf{M}_{R O} & =\{0.650 \mathbf{i}+19.75 \mathbf{j}-9.05 \mathbf{k}\} \mathrm{kN} \cdot \mathrm{m}
\end{aligned}
$$
