PSQ is a focal chord of the parabola
\[
y^2=12x.
\]
\(A\) and \(B\) are respectively the feet of the perpendiculars drawn from \(P\) and \(Q\) on the directrix of the parabola. If the length of \(AB\) is \(7\sqrt3\) and
\[
P=(3t^2,6t), \qquad (0<t<1),
\]
then \(t=\)