So we wan't to know how many fluid ounces are left in the bottle if Ollie drank 3/4 of a 16 fluid ounces bottle. We know he drank 3/4 of a bottle so what remained was 1/4 of juice in the bottle. Lets see how much is left: (1/4)*16=4. So there remained 4 fluid ounces of juice in the bottle.