A sample of nylon 6,6 has a number-average molar mass of $28000\mathrm{g}\mathrm{mo}{\mathrm{l}}^{-1}$. The repeat unit is $-[\mathrm{NH}-(\mathrm{CH}{}_2){}_6-\mathrm{NH}-\mathrm{CO}-(\mathrm{CH}{}_2){}_4-\mathrm{CO}]{}^{-}$, formula $\mathrm{C}{}_{12}\mathrm{H}{}_{22}\mathrm{N}{}_2\mathrm{O}{}_2$ (atomic masses C 12, H 1, N 14, O 16). Neglecting end groups, find the degree of polymerisation, defined as the number of repeat units per chain. Give the answer to the nearest integer.

Numerical answer type, answer in repeat units, tolerance 0.5.