Someone..Anyone help please ???ASAP 30 points ?

Determine whether the set of whole numbers is closed under addition. explain why the set is or is not closed. give an example.

Marcus and cody both leave the park at the same time, but in opposite directions. if cody travels 6 mph faster than marcus and after 4 hours they are 64 miles apart, how fast is each traveling? solve using rare times time = distance.

I’m still confused on how to work the percentages