I'm struggling in this question. Please help me explain, thank you so much!

1. Describe how an increase in the number of illegal immigrants entering the country would affect the U.S. PPF.
2. Describe how the discovery of a new oil field would affect the U.S. PPF.
3. Describe how a decrease in the unemployment rate would affect the U.S. PPF.
4. Describe how the declining rate of college enrollment would affect the U.S. PPF.