Estimate the total time and cost for excavation of a trench 30-in. wide with an average depth of 7 ft. The trench is 6,400 & long in common earth. A ladder-type trenching machine will be used with productivity of 25.9 ft/hr. A foreman and 2 laborers will assist the trenching operation. Cost: trenching machine@$85/hr., operator@$31/hr., laborer@$18/hr. and foreman@$34/hr.