a person plan to invest up to $20000 at bank1 or bank2. he want to invest at least $3000 in bank1, but not more than $16000; since bank2 doesnt insure more than $13000, he want to invest no more than this amount in bank2. The interest at bank1 is 8% and interest at bank2 is 12%. How much should he invest in each bank to earn the most interest?