Table: nature_of_america_stamps
Columns: ecosystem
date_of_issue
place_of_issue
no_stamps_in_sheet
face_value
printer

Question: When the face value is 42¢, what was the issue's date?
SQL: SELECT "date_of_issue" FROM nature_of_america_stamps WHERE "face_value" = '42¢'

Question: Which location has the ecosystem of kelp forest?
SQL: SELECT "place_of_issue" FROM nature_of_america_stamps WHERE "ecosystem" = 'Kelp Forest'

Question: How many stamps have a face value of 37¢ and were printed in the banknote corporation of america?
SQL: SELECT COUNT("no_stamps_in_sheet") FROM nature_of_america_stamps WHERE "face_value" = '37¢' AND "printer" = 'Banknote Corporation of America'

Question: Who was the printer of Estes Park, Colorado?
SQL: SELECT "printer" FROM nature_of_america_stamps WHERE "place_of_issue" = 'Estes Park, Colorado'

Question: The stamp was 39¢, who was the printer?
SQL: SELECT "printer" FROM nature_of_america_stamps WHERE "face_value" = '39¢'