c) Estimate the activity duration if the contractor decides to excavate the layer by drilling and blasting. The site is 200 ft by 400 ft and must be excavated to an average depth of 14 ft. Trial blasting indicates that 3 in holes drilled in a 10 ft rectangular pattern will provide the desired fracturing. A hole depth of 16 ft must be drilled to yield a 14 ft effective depth. The average drilling and blasting rate is estimated to be 200 ft/hr.