The table is \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \

\  x \	\ y \
\  1 \	\  6 \
\ 2 \	\  9 \
\ 3 \	\  12 \
\ 4 \	\  15 \

\

From the table x increases by 1, y increases  by 3. So, this is a linear function.

It represents a linear function.