Answer and Explanation:
The journal entries are shown below
On Dec. 31, 2018
Interest receivable $600
To Interest income $600
(Being accrued interest earned is recorded)
On Dec. 31, 2018
Interest income $2,400
To Retained earnings $2,400
(Being the closing of interest income is recorded)
On Jan. 31, 2019
Cash $900
To Interest receivable $600
To Interest income $300
(Being cash receipt of interest is recorded)