Need solving this problem: jamaal is planning to invest up to 23,000 in city bank or state bank. he wants to invest at least 1,000 in city bank, but not more than 4,000; since state bank does not insure more than $21,000, he wants to invest no more than this amount in state bank. the interest at city bank is 5%, and the interest at state bank is 12%. how much should he invest in each bank to earn the most interest?