An automobile company built two production lines at the same time. The first production line produced 1,000 vehicles in the first month, and then produced 100 more vehicles each month than the previous month; 500 cars are produced in each half month, and 50 more cars are produced in each half month than in the first half month. Then, how many months will it take for these two production lines to produce 20,000 cars in total?
某汽车公司同时建成两条生产线，第一条生产线第一个月生产了1000辆汽车，以后每个月比前一个月多生产100辆；第二条生产线第一个月的前半个月与后半个月各生产了500辆汽车，以后每半个月比前半个月多生产50辆，那么，这两条生产线共生产20000辆汽车需多少个月．
<gadget id="calculator">6 + 1</gadget>
<output>7</output>

<result>7</result>