The City of Omniville has two options for a viaduct. One is a permanent cement canal and the other a cast iron (CI) pipe. If details for the options are as shown, at what rate of interest should the city be indifferent to either choice?

	Cement Canal	CI PIPE
Initial cost	($5,000,000)	($4,000,000)
Life	Perpetual	25	years
Annual maintenance cost	$550,000	$700,000
Salvage	$0	$560,000
Initial Rate	11.0%		p. y.

	Possible answers:	35.04%,
		6.9%,
		10.66%, or
		16.31%?