2.1.22  A high school math department purchased Brand A calculators
for $80 each and brand B calculators for $95 each. It purchased a total of
20 calculators at a total cost of $1780. How many of each type of calculator
did the department purchase?

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2.1.39 A bank wishes to invest a $100,000 trust fund in 3 sources: bonds
paying 8%, certificates of deposit (CDs) paying 7%, and first mortgages paying
10%. (They are the lender in these mortgages.) The bank wishes to realize an
$8000 annual income from the investment. A condition of the trust is that
the total amount invested in bonds and CDs must be triple that invested in
mortgages. How much should the bank invest in each source?