Let the equation \( x(x+2)(12-k)=2 \) have equal roots. Then the distance of the point \( \left(k,\dfrac{k}{2}\right) \) from the line \( 3x+4y+5=0 \) is:
\( 5\sqrt{3} \)
\( 12 \)
\( 15 \)
\( 15\sqrt{5} \)