When we look at the costs of using dynamic arrays and linked lists, we notice some key differences.

1. Dynamic Arrays:

   • Cost to Add an Item (Append): On average, this is $O(1)$.
   • Sometimes, the array needs to grow bigger, which means it has to copy all its items. This process can take longer, or about $O(n)$ time, but it doesn’t happen all the time.

2. Linked Lists:

   • Cost to Add an Item (Append): This is always $O(1)$.
   • Adding a new item is simple because we just need to change some pointers.

To sum it up, both dynamic arrays and linked lists usually take about the same amount of time to add new items. However, dynamic arrays can be slower occasionally when they need to resize.