According to the definition of torque,

\(\vec{\tau}=\vec{r} \times \vec{F}\)

Given that,the force is

\(\overrightarrow{ F }=20 \hat{i}N\)

and the arm vector is

\(\overrightarrow{ r }=(0-3) \hat{ i }+(2-0) \hat{ j }+(0-0) \hat{ k }\)

\(\overrightarrow{ r }=(-3 \hat{ i }+2 \hat{ j }) m\)

Therefore,

\(\vec{\tau}=\overrightarrow{ r } \times \overrightarrow{ F }\)

\(\vec{\tau}=\left|\begin{array}{ccc}\hat{\imath} & \hat{ j } & \hat{ k } \\-3 & 2 & 0 \\ 20 & 0 & 0\end{array}\right|=(0-0)\)

\(\hat{i}-(0-0) \hat{\hat{j}}+(0-40) \hat{ k }\)

\(|\vec{\tau}|=40 N - m\)