A port authority intends to build a bridge and has two main options. a high level reinforced concrete bridge and a low level-steel bridge. the high level bridgehas an initial construction cost of £40 million, with maintenance costs estimated at £40,000 per annum. its asphalt road surface would have to be relaid every 10 years at a cost each time of £75,000. the low-level steel bridge and ancillary works are estimated at £35 million with maintenance costs estimated at £30,000 per annum. its road must be relaid every 10 years at a cost of £45,000 each time. use present worth analysis to compare the two options over a period of 50 years based on a rate of interest of 5% per annum.