A homeowner is planting hedges and begins to dig a 3-ft-deep trench around the perimeter of his property. After the fi rst weekend, the homeowner recruits a friend to help. After every succeeding weekend, each digger recruits another friend. One person can dig 405 ft3 of dirt per weekend. Th e fi gure at the right shows the dimensions of the property and the width of the trench. a. Geometry Determine the volume of dirt that must be removed for the trench. b. Write an exponential function to model the volume of dirt remaining to be shoveled after x weekends. Th en, use the model to determine how many weekends it will take to complete the trench.