S. 115BBE : Tax on specified income-Determination of tax in certain cases-Unexplained income-Rate of tax-Assessee did not maintain proper books of account-Excess stock and receivables on account of unaccounted sales and cash generated on account of unaccounted sales was found in survey-Assessee’s explanation accepted by survey party-Additional income surrendered by assessee not from unexplained source but from business proceeds-Under peculiar facts surrendered income to be taxed at normal rate applicable to business income and not at higher rate of sixty per cent: