Answer:
18 inch round pizza
Step-by-step explanation:
you need to find the price per inch and whichever pizza costs the least per inch, thats your best deal!
so for the 9- inch round you would divide $10.50 by how many inches there are which is 9 so each inch costs aproximately $1.16
for the 12- inch round, you will divide the price of $15 by the 12 inches of pizza which will equal out to $1.25
for the 18 inch round pizza, you will divide the price of $19 by the 18 inches which will equal out to about $1.05
so, going off of the price per inch of pizza, the 18 inch round pizza is giving you the best deal.