Answer: $27,000
Step-by-step explanation:
Even though for GAAP reasons, revenue is to be recognized only when earned as per the Accrual principle of accounting, this is not so for the calculation of taxable income.
Taxable income is to be calculated on cash basis which means that taxes are to be paid on revenue when the revenue is received in cash and not when it is earned.
As Ral Corp. received the money in 2020, they are to include the entire amount of $27,000 in their 2020 taxable income for rent revenue.