A water district wishes to compare alternative plans for additional water supplies, using a forty-year period of analysis and an interest rate of 6%.
 A gravity plan would require an investment of $5,000,000 for construction and
$20,000 per year for operation and maintenance.
 A pumping plan would require $3,000,000 for initial construction, an additional
investment of $500,000 in the tenth year, and $50,000 per year for operation
and maintenance. The pumping plan would also incur power costs of $100,000
per year for the first ten years and after connection to another source of demand
additional power costs of $100,000 per year.