Carla Vista Co. gathered the following information on power costs and factory machine usage for the last six months: Month Power Cost Factory Machine Hours January $28,600 15,900 February 36,410 21,600 March 33,100 18,800 April 26,440 15,200 May 24,100 13,600 June 20,900 10,600 Using the high-low method of analyzing costs, answer the following questions and show computations to support your answers. (a) What is the estimated variable portion of power costs per factory machine hour? (Round answer to 2 decimal places, e.g. 15.25.) Variable power costs per factory machine hour