Quinten and his friends ate \( \frac{6}{12} \) of the peach pie, which simplifies to \( \frac{1}{2} \).
To find out how many slices of the cherry pie they ate, we need to determine \( \frac{1}{2} \) of the cherry pie, which has 8 slices.
So, we calculate:
\[ \frac{1}{2} \times 8 = 4 \]
Therefore, they ate 4 slices of the cherry pie. The correct response is 4.