The time is taken by the boat to cover upstream distance \(=6\) hours

**Formula used:**

Upstream speed \(=u-v\)

Downstream speed \(=u+v\)

Where,

\(\mathrm{u}\), is the speed of the boat

\(v\), is the speed of the stream

Speed \(=\frac{\text { Distance }}{\text { Time }}\)

**Calculation:**

The upstream speed,

\[

\begin{aligned}

&\Rightarrow \mathrm{u}-\mathrm{v}=\frac{240}{6} \\

&\Rightarrow \mathrm{u}-\mathrm{v}=40 \mathrm{kmph} \quad-(1)

\end{aligned}

\]

The downstream speed,

\[

\begin{aligned}

&\Rightarrow \mathrm{u}+\mathrm{v}=\frac{240}{3} \\

&\Rightarrow \mathrm{u}+\mathrm{v}=80 \mathrm{kmph} \quad-(2)

\end{aligned}

\]

On subtracting the equation (1) from equation (2), we get,

\[

\begin{aligned}

&\Rightarrow 2 \mathrm{v}=40 \\

&\Rightarrow \mathrm{v}=20 \mathrm{kmph}

\end{aligned}

\]

The speed of the stream \(=20 \mathrm{kmph}\)

\(\therefore\) The speed of the stream is \(20 \mathrm{kmph}\).