To calculate U.S. net capital outflow, you can use the following formula:
\[ \text{Net Capital Outflow} = \text{Foreign Purchases of U.S. Assets} - \text{U.S. Purchases of Foreign Assets} \]
In this case, U.S. residents purchase $600 billion worth of foreign assets, and foreigners purchase $300 billion worth of U.S. assets:
\[ \text{Net Capital Outflow} = 300 \text{ billion} - 600 \text{ billion} = -300 \text{ billion} \]
A negative net capital outflow indicates that more capital is flowing into the U.S. than out. Therefore, the correct answer is:
d. U.S. net capital outflow is -$300 billion; capital is flowing into the U.S.