Final answer:
Marcella can use the equation c = 18.7 divided by 3 to find out how many carbohydrates she consumed.
Step-by-step explanation:
To find out how many carbohydrates Marcella consumed, she can use the equation c = 18.7 divided by 3, which is Option 1. Since Marcella ate one cup of air-popped popcorn and the nutritional facts state that air-popped popcorn contains 3 cups of carbohydrates, dividing 18.7 by 3 will give her the amount of carbohydrates she consumed.