。
What was your total income for the previous year?
Literal
Previous-year [attributive-の] total-income-amount [topic-は] how-much [polite-suppositional-でしょうか].
Administrative/bureaucratic register typical of a tax form or official interview. 前年 ('previous year') is more formal than 去年. 総所得金額 ('total income amount') is a Sino-Japanese compound of the kind you meet in tax and legal documents. The softened question ~でしょうか is more polite than bare ~ですか, adding a note of deference to a formal inquiry.