Sweeney & Allen, a large marketing firm, adjusts its accounts at the end of each month. The following information is available for the year ending December $31$:

A bank loan had been obtained on December $1.$ Accrued interest on the loan at December $31$ amounts to $$1,500.$ No interest expense has yet been recorded.

Depreciation of the firm's office building is based on an estimated life of $30$ years. The building was purchased four years ago for $$450,000.$

Accrued, but unbilled, revenue during December amounts to $$75,000.$

On March $1,$ the firm paid $$2,400$ to renew a $12-$month insurance policy. The entire amount was recorded as Prepaid Insurance.

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$5.$ The firm received $$15,000$ from King Biscuit Company in advance of developing a six$-$month marketing campaign. The entire amount was initially recorded as Unearned Revenue. At December $31,$$$9,000$ had actually been earned by the firm.

$6.$ The company's policy is to pay its employees every Friday. Because December $31$ fell on a Wednesday, there was an accrued liability for salaries amounting to $$1,900.$

a$.$ Record the necessary adjusting journal entries on December $31.$

b$.$ By how much did Sweeney & Allen's net income increase or decrease as a result of the adjusting entries performed in part a$?($Ignore income taxes.$)$