A marketing research firm has these requirements for validity of a market survey:

1. Survey at least 5,000 U.S. households
2. Survey at least 1,000 households whose heads are 30 years old
3. Survey at least 750 households whose heads are between 31 and 50
4. Ensure that no more than 20% of those surveyed are 51 years of age

COST PER PERSON SURVEYED ($)
Age <=30	Age 31	Age >= 51
8	9	7.5

Find the minimum interview costs considering the above business rules.