If you can create it into a common denominator then the rest is simple. Tamika needs 2 1/2 cups of sugar to make the cake. That is 5/2. She has already put in 2/3. We can use common denominator and bump the denominator up to 6. Meaning that she needs 15/6 cups to make the cake and she put in 4/6 cups in the bowl. Meaning she would need 11/6 more cups.