40 cents an ounce, since you firstly convert the ounces into a decimal value of9 3.5. Then since you have to find out the unit rate, or cost per ounce, you will then divide the price ($1.40) by the ounces (3.5). This will then get you to 1.4/3.5, which then when calculated gives the answer of .4, equivalent to 40 cents.
