So the unit rate is basically how many ounces in 1 cup?
So since there are 64 ounces in 8 cups, you can just divide by 8, to find how many sets of 8 there are in 64.
64 = 8
64 / 8 = 8 / 8
8 = 1
So there are 8 ounces in 1 cup, which is your unit rate.