Recall that a reflection across the line x=k (with k a real number) transforms the point (x,y) as follows:
[tex](x,y)\rightarrow(2k-x,y).[/tex]Therefore, the image of F(6,-3) after the reflection across the line x=3 is:
[tex](2\cdot3-6,-3)=(0,-3)\text{.}[/tex]Answer: (0,-3).