To determine how many slices of the cherry pie Quinten and his friends ate, we first need to find the fraction of the peach pie they consumed. They ate 6 out of 12 slices of the peach pie.
The fraction of the peach pie they ate is:
\[ \frac{6}{12} = \frac{1}{2} \]
Since they ate the same fraction of the cherry pie, we now calculate how many slices of cherry pie correspond to this fraction. The cherry pie has 8 slices, so half of the cherry pie is:
\[ \frac{1}{2} \times 8 = 4 \]
Therefore, they ate 4 slices of the cherry pie.
The answer is 4.