Answer
$\text{Constant of variation: }
k=0.17
\\\text{Equation of variation: }
y=0.17x
$
Work Step by Step
Since $y$ varies directly as $x$, then $y=kx.$ Substituting the known values of the variables, then,
\begin{array}{l}\require{cancel}
0.51=k(3)
\\\\
\dfrac{0.51}{3}=k
\\\\
0.17=k
\\\\
k=0.17
.\end{array}
Hence, the variation has the following properties:
\begin{array}{l}\require{cancel}
\text{Constant of variation: }
k=0.17
\\\text{Equation of variation: }
y=0.17x
.\end{array}
