According to an estimate by thomas jefferson, approximately how many virginia slaves ran away from their masters in 1778?

The Subjects of the most Christian King shall pay no other Duties or Imposts in the Ports, Havens, Roads, Countries, Islands, Cities, or Towns of the said united States or any of them, than the Natives thereof, or any Commercial Companies established by them or any of them, shall pay, but shall enjoy all other the Rights, Liberties, Priviledges, Immunities, and Exemptions in Trade, Navigation and Commerce in passing from one Part thereof to another, and in going to and from the same, from and to any Part of the World, which the said Natives, or Companies enjoy.