The Golden Gate Bridge in San Francisco was financed with construction bonds sold for $34 million in 1931. These were 40-year bonds, and the $34 million principal plus almost $38 million in interest were repaid in total in 1971. Assume the construction bonds had been retired as an annuity (i.e. equal uniform annual payments had been made to repay the $34 million). The interest is also paid uniformly. What interest rate was paid on the construction bonds?