Final answer:
Sarah needs an additional 1/8 cup of sugar to fulfill the requirements for both the cake and cookies.
Step-by-step explanation:
Sarah has a total of 15/16 cups of sugar, and the cake requires 3/8 cup while the cookies need 3/5 cup. First, finding a common denominator to facilitate calculations, the least common multiple of 8 and 5 is 40. To adjust the sugar requirements, we convert the amounts needed for the cake and cookies to 40ths: 3/8 becomes 15/40, and 3/5 becomes 24/40. Adding these amounts together (15/40 + 24/40) gives us 39/40, which represents the combined sugar needed for both items.
Since Sarah has 15/16 cups (which is equivalent to 30/40 in 40ths), subtracting 30/40 from 39/40 reveals the deficit, resulting in 9/40. Simplifying 9/40 gives us 1/8, indicating that Sarah needs an additional 1/8 cup of sugar to meet the requirements for the cake and cookies.
The correct answer is B. She needs 1/8 of a cup of sugar.