Which sentence correctly forms the plural of the number 6?
a. herb's zip code has four 6's and a 2.
b herb's zip code has 4 6 and a 2.
c. herb's zip code has four 6's and a 2.
or d. herb's zip code has four 6's and a 2.
plz im stuck on this so hard its almost been an hour of me trying to finish : ) you!