It is important to know that the definition of the parabola is
[tex]x^2=4py[/tex]Where p represents the focus coordinate, so p = 3. Also, we know that y = 12, let's find x
[tex]\begin{gathered} x^2=4\cdot3\cdot12 \\ x=\sqrt[]{144} \\ x=12 \end{gathered}[/tex]But, the wide of the lamp is 2x, so
[tex]2x=2\cdot12=24[/tex]