Answer
Input - Output
6 - 18
7 - 21
8 - 24
Work Step by Step
a) We make a table for the inputs and outputs:
\begin{array}{|c|c|} \hline \text{Input} & \text{Output}\\\hline 1 & 3 \\ \hline 2 & 6 \\ \hline 3 & 9 \\ \hline 4 & 12 \\ \hline 5 & 15 \\ \hline
\end{array}
We notice that each output is $3$ times the input:
$$\text{Output} = 3\cdot \text{Input}$$
b) We calculate the outputs for the inputs $6$, $7$ and $8$:
$\text{Input}=6\Rightarrow \text{Output}=3\cdot 6=18$
$\text{Input}=7\Rightarrow \text{Output}=3\cdot 7=21$
$\text{Input}=8\Rightarrow \text{Output}=3\cdot 8=24$
