Allow me to step in and check why there's a -$15.30 on the Net Operating Income and Net Income, FP98.
You can click the -$15.30 on the Profit and Loss report to see where the amount is coming from. After clicking the amount, it will open the Profit and Loss Detail report.
Please see the sample screenshots below.

From there, you'll see how QuickBooks calculated the amount that appears on the Net Operating Income and Net Income section. The negative amount shows that there are expenses in that period.
I suggest discussing this with your accountant before writing off inventory items given as promotional samples. This is to make sure you the amounts on your reports are accurate and your books have correct records.
I'm adding these articles to learn how QuickBooks handles your inventory.
Stay in touch with me you have additional questions about the amounts showing up on your Profit and Loss report. I'll be right here to guide you.