Okay, so when dealing with unit rates you want to see how much you have of your main measurement. In this case your main measurement is ounces. Since you have 16 and 32 you are going to divide your dollar amount by those and round to the nearest tenth.
Here are the equations that need to be used. Figure out the answers to them and round. This will give you your answer
3.98/16=
5.98/32=