Final answer:
To add a footer or header in an Excel worksheet, navigate to the Page Setup group on the PAGE LAYOUT tab and click on the Header & Footer button.
Step-by-step explanation:
To insert a footer or header in a Microsoft Excel worksheet, you don't use the INSERT tab; instead, you go to the PAGE LAYOUT tab, where you will find the option in the Page Setup group. Specifically, you will first need to navigate to the PAGE LAYOUT tab on the Excel ribbon. Next, you'll locate the Page Setup group within this tab. Then, click on the Header & Footer button to enter or edit headers and footers on your worksheet.
The correct answer to the question is: C) Page setup group on the PAGE LAYOUT tab.