Answer:
Stacy ate the least amount of pizza.
Explanation:
Since each friend ate different fractions of pizza, in order to compare them, you would need to find a common denominator for all of the fractions. To find the common denominator, you need to find the least common multiple (LCM) of all four numbers: 3, 2, 8 and 6. The LCM would be 24. Now, convert all of the fractions to a denominator of 24 by multiplying the numerator and denominator by the same factor:
Stacy:

Alexa:

Tenaya:

Natalie:

Since Stacy only had 8/24, or the lowest numerator of '8', then she ate the least amount of pizza.