Final answer:
The investment in Aquolina is $10 billion.
Step-by-step explanation:
To calculate the investment in Aquolina, we need to use the equation: GDP = consumption + investment + government spending. We are given that the GDP is $20 billion, government purchases are $3 billion, and private saving is $4 billion. To calculate investment, we can rearrange the equation to solve for investment: investment = GDP - consumption - government spending - private saving. Plugging in the known values, we have: investment = $20 billion - $3 billion - $3 billion - $4 billion = $10 billion.