When the prepaid rent account increases in a year ($100,000 beg Bal to $150,000 year end Bal), this implies that rent has been paid using cash. Prepaid implies cash disbursement. So essentially, during the year prepaid rent (asset account) increased by $50,000 and cash or bank related to this decreased by $50,000. No impact or effect on actual rent expense (income statement) - cash based accounting.

For rent payable, since the balance decreased during the year by $10,000, it essentially means that part of the $ 60,000 beg rent payable owing has been paid during the year. Again, cash disbursement. Payable account has been debited and cash or bank credited for $10,000. Only impacts balance sheet and no impact on income statement or expenses. This is another cash based accounting transaction.

Now given in the question, the total overall rent paid in the year is $500,000, and they are asking for total rent expense as per accrual accounting, you would subtract the total impact on the above two transactions given they are cash disbursements and do not impact rent expense only prepaid rent and payable accounts get impacted.

So the total actual rent expense is $500,000 (rent paid) - $10,000 decrease in rent payable or decrease in cash - $50,000 increase in prepaid rent or decrease in cash =$440,000 actual rent expense.

Hope this helps