16.
8 inch diameter -> 4 inch radius -> 50.2 in^2 area of the pizza.
the ratio of cost to size of first pizza is 0.199 $ per square inch of pizza.
14 inch diameter -> 7 inch radius -> 153.9 in^2 area of the pizza.
the ratio of cost to size of first pizza is 0.103 $ per square inch of pizza.
Since the 14 inch diameter pizza has a lower cost (0.103 $) than the 8 inch diameter pizza (0.199 $), the 14 inch diameter pizza is the "better buy".
17.
the circumference will double, and the area will multiply by 4!