What do I debit and Credit for interest earned but not recorded 250?
Accrued Interest expense 750?
Aging of Accounts Receivable showed and estimated 55,000 to be collectible?
Income tax expense 20%

dr. interest expense 750
cr. interest payable 750
to record unrecorded interest expense

dr. Bad debts expense 55000
cr. allowance for doubtful accounts 55000
to record allowance for doubtful accounts

the tax expense amount should be derived by multiplying the taxable net income by 20%
dr. income tax expense xx
cr. income tax payable/cash xx

To answer your first question:
What do I debit and Credit for interest earned but not recorded 250?

Dr. Interest Receivable 250
Cr. Interest Revenue 250