Total length of the ribbon,
→ 12 feet
Total ribbon used by Holy,
→ 3.5 feet
Now we have to,
find the maximum length of ribbon, that holly can use to wrap the rest of her gift.
The formula we use,
→ Length of ribbon - Ribbon used by Holy
Let's find the required value,
→ 12 - 3.5 = 8.5 feet
Therefore, the length of ribbon holly can use to wrap the rest of her gift is 8.5 feet.