For this question, we want to find out the greatest amount of area of pizza for the least amount of money:
So we have two pizzas with a 10 in. diameter. Let us take one of those pizzas.
The formula for area of a circle is
; So the area for one of these 10 in. pizzas would be 
or 25
.
We have two of these pizzas, so the total area that we would get with $14 would be 25*2 or 50.
For the second case, we have one pizza with a 14 in. diameter.
The area of this pizza will be
or 49.
So for $15 we can buy 49 worth of pizza.
The best deal would be to buy the two medium pizzas of 10 inch diameter, because for $14, you get 50.
So we have two pizzas with a 10 in. diameter. Let us take one of those pizzas.
The formula for area of a circle is
We have two of these pizzas, so the total area that we would get with $14 would be 25
For the second case, we have one pizza with a 14 in. diameter.
The area of this pizza will be
So for $15 we can buy 49
The best deal would be to buy the two medium pizzas of 10 inch diameter, because for $14, you get 50