Let $\mathrm{A}\mathrm{B}$ is the focal chord of a parabola and $\mathrm{D}$ and $\mathrm{C}$ be the foot of the perpendiculars from $\mathrm{A}$ and $\mathrm{B}$ on its directrix respectively. If $\mathrm{C}\mathrm{D}=6$ units and area of trapezium $\mathrm{A}\mathrm{B}\mathrm{C}\mathrm{D}$ is $36$ square units, then the length (in units) of the chord $\mathrm{A}\mathrm{B }$is