firm has a December $31$ fiscal year end. Provide the required journal entry for each of the following situations. $($Omit explanations and dates.$)$

a$.$ On September $1,$ the company collected rent in advance for the next six months and made the following entry: Dr $-$ Cash and Cr $-$ Deferred Rent Revenue, $$6,000.$ What is the adjusting entry on Dec $31?$

b$.$ On December I, the company signed a deal to provide services for $$10,000.$ By the end of the year, half the work is done, but no invoice has been sent to the client. What is the adjusting entry on Dec $31,$ if any?