Econ Q

4 yrs ago purchased machine $500k, est life 10yrs For accounting purposes depreciated $50k annually Being used to manufacture a particular product and has no alt use or scrap val Revenue generated is $650k Annual cost of factors of production, other than dep, employed to generate that rev is $600k Should the company continue to use the machine: 1) Yes 2) No cos operating costs are equal to operating revs 3) No cos the purchase price of the machine is a sunk cost 4) No cos the opp cost of opreating the machine is zero. The answer is A, can someon please explain WHY?? Thanks