Answer
$20$
Work Step by Step
Find the scalar, $4\left( \mathbf{u}\cdot \mathbf{v} \right)$ as,
$\begin{align}
& 4\left( \mathbf{u}\cdot \mathbf{v} \right)\mathbf{=}4\left[ \left( 2\mathbf{i-j} \right)\cdot \left( 3\mathbf{i+j} \right) \right] \\
& =4\left[ 2\cdot 3+\left( -1 \right)\cdot 1 \right] \\
& =4\left( 6-1 \right) \\
& =4\times 5
\end{align}$
Solve ahead to get the result as,
$\begin{align}
& 4\left( \mathbf{u}\cdot \mathbf{v} \right)=4\times 5 \\
& =20
\end{align}$
Hence, the scalar of $4\left( \mathbf{u}\cdot \mathbf{v} \right)$ is $20$.
