An L – shaped structure can be built for the service contemplated at a cost of $180,000, but an addition to this building will be necessary for storage, fifteen (15) years hence, at a cost of $100,000. A T-shaped structure can be built at the present time which will furnish adequate space for the entire period of planning, at a cost of $250,000. Both types of structures are of permanent construction, so that depreciation may be neglected in a comparison of costs. With interest at 6%, show which is the more economical plan for construction.