Thank you for the follow-up questions, @beginner-1.
I can share with you some additional information about managing items in QuickBooks Online (QBO).
The system follows the amounts you've entered per line when recording sales transactions. That said, the amount on the second item won't affect the price of the first one.
I've added this screenshot for your visual reference.
To learn more about tracking inventories, and adding products in QBO, you may check out these articles:
Also, here's a link you can open for an additional guide while managing your sales transactions.
If you have any other questions, please feel free to notify me by adding a comment below. I'm more than happy to help. Have a great day!