Easy, to find the unit cost, divide the price with the ounces.
For the 20-oz bottle of soda that is $1.79, divide 1.79 by 20 oz.
20/1.79= $11.17
For the 32-oz bottle, do the same.
32/3.49 = $9.17
The unit price of the 20-oz bottle would be $11.17, meanwhile the 32- oz bottle would have a unit price of $9.17.
The soda with the lower unit cost would be the larger sized bottle.