Answer:
The 18 inch slice is bigger because it has a larger area than the 12 in slice.
Explanation:
Find the radius of each pizza then find the area of each pizza.
The radius is half the diameter
The 12 inch pizza has a diameter of 12 in. Half of 12 in. is 6 in.
The 18 inch pizza has a diameter of 18 in. Half of 18 in. is 9 in.
Now find the area of each pizza. Then find the area of each slice by dividing the area by the number of slices.
12 in pizza
18 in pizza

The 18 inch slice is bigger because it has a larger area.