The 16 inch diameter leads to a 8 inch radius (cut the diameter in half). So r = 8 is plugged into the area of a circle formula to get
A = pi*r^2
A = pi*8^2
A = pi*64
A = 64pi .... which is the exact area in terms of pi
We'll use this value later, so let's call it A1 = 64pi
Repeat for the other pizza. We have a 12 inch diameter mean the radius is r = 6 so its area would be...
A = pi*r^2
A = pi*6^2
A = pi*36
A = 36pi
We'll use this value later, so let's call it A2 = 36pi
Now subtract the two areas (large - small) to get the difference in areas which we'll call D
D = A1 - A2
D = 64pi - 36pi
D = (64-36)pi
D = 28pi
The difference in the two areas is exactly 28pi square inches
Now use a calculator to find that 28*pi = 28*3.1415926535898 = 87.964594 approximately if you were to round to 6 decimal places
Approximate answer: 87.964594 square inches
note: I went with the approximate answer because it's probably easier to visualize a fractional or decimal part of a pizza better than some number in terms of pi
