Product is a 12 ounce bottle of generic mouthwash that sells $4.39 product b is a 24 ounce bottle of mouthwash that cost $2.79 which is the better buy. show the math problem step by step.

Hi there,
To compare we can look at the amount of (ounces)
A: 12         B:24
so as it appears B wins this part
Now price 
A: $ 4.39       B:$2.79
A is relatively expensive than B
B is cheaper with more ounces
A is less ounces and relatively expensive
which one would you buy?