If anyone could explicitly show me the steps of how this substitution works I'd be v. grateful
$\displaystyle
\frac{{dy}}
{{dx}} = \frac{{x^2 + y^2 + 9xy}}
{{9x^2 }} \Rightarrow \frac{{dy}}
{{dx}} = \frac{1}
{9}(1 + (\frac{y}
{x})^2 ) + \frac{y}
{x}
$