Final answer:
Granite Slab LLC's required taxable year-end is December 31, influenced by its members with the highest profit percentages, Nelson Black and Brittany Jones, whose tax year-ends correspond to that date.
Step-by-step explanation:
The required taxable year-end for Granite Slab LLC is determined based on the tax year-ends of its members. The Internal Revenue Service (IRS) has guidelines that require a partnership to conform its tax year to its members or to the majority interest in partnership profits and capital.
In this case, the members with the highest profit percentages, namely Nelson Black and Brittany Jones, have a taxable year-end of December 31. Therefore, the required taxable year-end for Granite Slab LLC would logically be December 31, as this would represent the majority interest in profits, which sets the standard for the whole LLC unless a business reason is stated otherwise or a specific tax ruling is applied.