From the given right triangle what is the value of $3 \sin^2 \varphi \, \sec \varphi$ in terms of $x$.

$\sin \varphi = \dfrac{x}{\sqrt{x^2 + 9}}$

$\sec \varphi = \dfrac{\sqrt{x^2 + 9}}{3}$
 

 

$\begin{align}
3 \sin^2 \varphi \, \sec \varphi & = 3 \cdot \left( \dfrac{x}{\sqrt{x^2 + 9}} \right)^2 \cdot \dfrac{\sqrt{x^2 + 9}}{3} \\
\\
& = \dfrac{x^2}{x^2 + 9} \cdot \sqrt{x^2 + 9} \\
\\
& = \dfrac{x^2}{\sqrt{x^2 + 9}}
\end{align}$