CREATE TABLE table_name_70 (ngc_number INTEGER, constellation VARCHAR(255), declination___j2000__ VARCHAR(255))
what is the ngc number when the constellation is leo and the declination (j2000) is °42′13″?
    
SQL: SELECT AVG(ngc_number) FROM table_name_70 WHERE constellation = "leo" AND declination___j2000__ = "°42′13″"