David manages the family farm he has several packages of fertilizer for his new grain crop the old packages contain 50 lb of long-term growth supplement and 60 lb of weed killer the new packages contain 65 lb of long-term growth supplement and 45 lb of weed killer using past experience David estimates that he needs 3,125 lb of long-term growth supplement and 2,925 lb of weed killer for the fields how many old packages of fertilizer and how many new packages of fertilizer should he use