Using Okun's law, fill in the four pieces of missing data in the table below. All of the following data are hypothetical.

$\backslash$table$[[$Year$,$Real GDP$,\backslash$table$[[$Potential$],[$GDP$]],\backslash$table$[[$Natural$],[$Unemployment$],[$Rate $(\%)]],\backslash$table$[[$Actual$],[$Unemployment$],[$Rate $(\%)]]],[2015,15,680,16,000,6,(a)$