We are asked to determine the unit price of two different packages. The unit price is determined by dividing the price of an item over the quantity used to measure that item at the given price. In this case, the unit of measure is "ounce", therefore, we need to determine the price per ounce. The first unit price is determined by dividing the price of $3.19 for 11.5 ounces, like this:

Since we are told to round to the nearest cent we take the first two digits after the decimal point and we add 1 to the second digit if the third digit is equal to or greater than 5.
Now we use the same procedure to determine the second unit price:

Since the unit price for the 30.6 ounces package is less than the price for the 11.5 ounces package this means that the second package is a better buy.