Answer
$y$ varies directly with $x$. The constant of variation is $7$.
The function rule is $y = 7x$.
Work Step by Step
To find the rule, we plug the $x$ values and $y$ values into the ratio $\dfrac{y}{x} = k$ to see if each set of $x$ and $y$ have the same constant of variation ($k$). If they do, then $y$ varies directly with $x$:
$\dfrac{14}{2} = \dfrac{21}{3} = \dfrac{35}{5} = 7$
Each ratio can be simplified to $7$; therefore, the constant of variation is $7$, and $y$ varies directly with $x$.
The function rule is $y = 7x$.