A nutritionist is creating a special blend of nuts and dried fruit. Each ounce of nuts contains $150$ calories, and each ounce of dried fruit contains $100$ calories. The nutritionist wants to create a blend that contains $n$ ounces of nuts and $f$ ounces of dried fruit, with a total of $C$ calories. The equation $150n+100f=C$ represents this situation. If the nutritionist used $8$ ounces of nuts and the total blend contained $1600$ calories, how many ounces of dried fruit were used?