Don't understand this question, please help.

Suppose government spending was $3.90 trillion, tax revenue was $4.50 trillion. GDP was $14.02 trillion, and total consumer spending was $10.75 trillion. Instructions: Round your answers to two decimal places and include a negative sign if necessary. a. If the economy has no exports or imports, what was the national savings? 85 trillion. b. How much was public savings? $ trillion. c. How much was private savings? $ trillion