A contractor is installing girders for a lid across SR 520 on the east side of Lake Washington (see WSDOT time lapse video). The facts of girder installation: It takes the contractor, on average, 30 minutes (0.5 hours) to install one girder if they work straight through the entire 30 minutes without any breaks for any reason. In other words, if ALL their work is productively used to set the girder. There are 42 girders to install in the lid. Installation efficiency is 45 minutes per hour (they average 45 minutes of productive work per hour, the rest is for crane repositioning, waiting for girder delivery, etc.). Think carefully and logically about how you apply this factor. It takes 2 hours to mobilize the construction site and set up traffic control before the first girder is installed. It takes 1 hour to demobilize the construction site and remove traffic control after the last girder is installed. How many hours (rounded to the nearest whole hour) does the contractor need to complete the installation including mobilization, demobilization and traffic control setup/removal