In the case of (a), if an assessment official has reason to believe that the taxpayer underreports the amount of income, he shall have the power to assess the income according to the reasonable rent of property under normal circumstances, and the amount so assessed shall be deemed assessable income of the taxpayer. In such case, the taxpayer may appeal against the assessment and shall apply the provisions on appeals under Part 2, Chapter 2, Title 2 mutatis mutandis.