please explain with the answer why we are adjusting as I am very very awful with adjusting... A bit of the theory of why would be really appreciated

(chp 3) Prepare adjusting and correcting entries as of year-end December 31. Also, which of these could be reversed? 14,000 40.000 300 4,500 1.800 5,000 80,000 Acc2271 Final Review Trial Balance December 31 Cash Accounts Receivable Allowance for Doubtful Accounts Inventory Prepaid Rent Investment Plant and Equipment Accumulated Depreciation Accounts Payable Bonds Payable Common Shares Retained Earnings Sales Cost of Goods Sold Delivery Expense Salaries and Wages Expense Interest Expense Rent Revenue Miscellaneous Expense (what on earth??? NEVER!!!) Insurance Expense 12,000 8.000 15,000 25,000 45,030 180.000 100,000 1,000 42,000 2.000 10,000 430 4,000 $295.030 $295.030 a. Insurance expense is $4000. "Policy A" taken out on July 1 for 1 year term $1000, "Policy B" taken out on January 1 for a 3-year term $3000 b. Rent Revenue includes a payment for services for 4 months of $4000 of equal service each month, received November 1 c. Salaries accrued but not paid as of Dec 31 $1250 d. Prepaid Rent is the whole amount for rent for Dec & Jan $1800 e. Jan 1 had 100,000 in capital assets, no acquisitions during the year, Dec 31 balance in capital assets 80,000, rate of depreciation is 10%, disposals and acquisitions are at this rate. What is depreciation expense? f. Incorrectly recorded as a credit a payment of an Accts Rec. for $2000 to sales g. Estimated that 5% of Accounts Receivable will become uncollectible, the allowance method is used. h. Sept 1 you purchased $5,000 10% bond. Interest payment dates are August 30 and February 28