Electrochemistry

The molar conductivity of 0.007 M acetic acid is $20\mathrm{S}\mathrm{c}{\mathrm{m}}^2\mathrm{mo}{\mathrm{l}}^{-1}$. What is the dissociation constant of acetic acid? (Given ${\lambda }_{{\mathrm{H}}^{+}}^{\circ }=350\mathrm{S}\mathrm{c}{\mathrm{m}}^2\mathrm{mo}{\mathrm{l}}^{-1}$ and ${\lambda }_{\mathrm{C}{\mathrm{H}}_3\mathrm{CO}{\mathrm{O}}^{-}}^{\circ }=50\mathrm{S}\mathrm{c}{\mathrm{m}}^2\mathrm{mo}{\mathrm{l}}^{-1}$)