In a formal outline what should roman numerals represent?

Main Ideas.

Explanation:

Outlining in an essay displays the map of an essay. It reflects the central idea of each paragraph and arranges information in order to convey an effective message to the readers. It is crucial to organize an idea, visualize the structure of the thesis and develop the main points in a logical order.  

The formal outline employs the Roman numeral to represent the main ideas. This type of outline usually begins with a roman numeral that differentiates it from an informal outline. Thus, the last option best exemplifies the appropriate function of roman numerals, i.e. to display the main points that develop the thesis statement.

you can buy 12 peppers or less. $1.50*12 = $18