问题某化工企业每月收入为80万元.从今年起,若不改善生产环境,则在生产过程中产生的污水交由污水厂处理,每月上交定额5万元的治污费.如果该企业从今年1月份起投资300万元增加回收净化设备以改善生产环境,降低企业生产成本.已知该设备每月的运转费用是0.2万元.问:经过多少个月,投资开始见效,即投资改造后的月累计纯收入多于不 Problem A chemical company’s monthly income is 800000 yuan .From this year, if not improve the production environment, the sewage produced in the process of production by the sewage treatment plant, a monthly pay a fixed amount of 50,000 yuan pollution control costs. Since January this year, the company invested 3 million yuan to increase the recovery of purification equipment to improve the production environment and reduce production costs.It is known that the monthly operation cost of the equipment is 0.2 million.Q: After months, the investment started to bear fruit, That is, the accumulated net income after the investment reform is more than no