Hello everyone.
Can you please tell me if the entries I made were correct.
If not, can you help me with the right answers.

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Dec01 Contracted with the local newspaper for 3 months of advertising and paid in full the total fee of 600.
Dr -- Advertising Expense 600
Cr -- Cash 600

Dec02 Billed C. company and F. Company for services rendered, 150.
Dr -- Accounts receivable 150
Cr -- Fee Income 150

Dec03 Paid 700 on account for office equip. purchased in June.
Dr -- Accounts Payable 700
Cr -- Cash 700

Dec05 Received a check for 30 representing interest due on marketable securities.
Dr -- Cash 30
Cr -- Interest income 30

Dec05 Received a bill from S. Company for outside services performed, 35. Charge is to be recorded as a miscellaneous expense of doing business.
Dr -- Miscellaneous expense 30
Cr -- Accounts payable 30

Dec09 Billed V. client for services rendered, 300.
Dr -- Accounts Receivable 300
Cr -- Fee Income 300

Dec11 Purchased a tract of Land for 6000 by issuing a note payable for 4000 and paying the balance in Cash.
Dr -- Land 6000
Cr -- Notes Payable 4000
Cr -- Cash 2000

*******

Comment / suggestion needed.
Thank you!

The first entry I would do it as follows:

Debit Prepaid Advertising for 600
Credit Cash for 600

After the newspaper provides the advertising then the entry would be:

Debit Advertising Expense for 600
Credit Prepaid Advertising for 600

The other entries look correct.