Answer: $56,000
Explanation: GDP refers to the total market value of final goods and services produced in a nation. According to the income method, it is the sum of all factors incomes by factors of production located within a country.
The salary of the homemaker is a factor income for her. In addition to this, the money paid for professional child care services will be a factor income for the provider of those service.
Thus, total value of GDP is $40000 +$16000 =$56,000