$3$ years are years $1,2$ and $3.$

$\backslash$table$[[$Employee$,\backslash$table$[[$Departure year: year $1,],[$year $2,$ year $3,$ or after$],[$year $3?]],\backslash$table$[[$Turnover cost from the$],[$employee within next $3],[$years$]],\backslash$table$[[$years$]]]]$