Answer:
Part 1) The units rates are
A)

B)

C)

D)

Part 2) The best buy is the size 48 1/4 oz
Explanation:
we know that
To find out the unit rate divide the total cost by the total volume
Part 1) Calculate the unit rate for each size
case A) we have
8 1/2 ounce bottle costs $0.99
Convert mixed number to an improper fraction

Find the unit rate

case B) we have
18 2/2 oz. bottle costs $1.49
Convert mixed number

Find the unit rate

case C) we have
48 1/4 oz. carton costs $2.49
Convert mixed number to an improper fraction

Find the unit rate

case D) we have
64 3/4 oz. carton costs $3.75
Convert mixed number to an improper fraction

Find the unit rate

Part 2) which size is the best buy
we know that
The best buy is the one with the smallest unit rate
so

The best buy is the size 48 1/4 oz