Answer: the guys' skateboards
Step-by-step explanation:
The possessive case is formed by adding ’s or sometimes just the apostrophe to a noun. There are a few different ways to form the possessive of a noun.
If the noun doesn’t end with an s, ’s is added to the end of the noun:
the guy's skateboards.This means there is only one guy.
This is the way to the men’s room. In this case, the noun is plural but ´s is still added because men does not end in s.
When a plural noun ends in s, just the apostrophe is added:
the guys' skateboards