Answer:
The angle of slice is approximately 16°.
Explanation:
The slice of pizza represent the sector of a circle.
The area of a sector is:

Here,
r = radius of the circle
Φ = angle in radians
Given:
A = 20 inches²
r = 12 inch
Compute the angle of the slice as follows:



The angle us 0.2778 radians.
Convert the angle into degrees as follows:

Thus, the angle of slice is approximately 16°.