You need a line with this equation:
[tex]y=mx+b[/tex]Where m is the slope and b is the intercept.
We know that it has to be perpendicular to
[tex]y=-\frac{1}{2}x+9[/tex]Two lines are perpendicular if their slopes are the opposite and reciprocal of each other. Therefore we have that the slope m has to be 2. For now we have:
[tex]y=2x+b[/tex]To find the intercept we use the given point Q(6,3). If we replace these values into the equation above, we can clear b:
[tex]3=2\cdot6+b[/tex][tex]b=3-2\cdot6=3-12=-9[/tex]Now we have the full equation of the line:
[tex]y=2x-9[/tex]