The rule of a reflection across the y-axis is
[tex](x,y)\rightarrow(-x,y)[/tex]
So, let's transform each vertex.
[tex]\begin{gathered} A(4,4)\rightarrow A^{\prime}(-4,4) \\ B(3,-1)\rightarrow B^{\prime}(-3,-1) \\ C(1,-2)\rightarrow B^{\prime}(-1,-2) \end{gathered}[/tex]
Now, we graph the reflection, the image below shows it
