A certain unit organizes employees to go to the Shanghai World Expo through a travel agency. The following is a paragraph about the charging standards of the tour guide and the tour guide of the travel agency: Tour leader: What is the charging standard per person? Tour guide: If the number of people does not exceed 30, the per capita tour fee is 120 yuan. Team Leader: How about a discount for more than 30 people? Tour guide: If there are more than 30 people, the per capita tourism fee will be reduced by 2 yuan for each additional person, but the per capita tourism fee should not be less than 90 yuan. The unit paid a total of 4,000 yuan to the travel agency after organizing a group to visit the World Expo according to the charging standard of the travel agency. Based on the above information, please tell me how many people from this unit visited the World Expo this time?
某单位通过旅行社组织职工去上海世博会，下面是领队与旅行社导游收费标准的一段话：领队：每人的收费标准是多少？导游：如果人数不超过30人，人均旅游费用为120元．领队：超过30人怎样优惠呢？导游：如果超过30人，每增加1人，人均旅游费用就降低2元，但人均旅游费用不得低于90元．该单位按旅行社的收费标准组团参观世博会后，共支付给旅行社4000元．请你根据上述信息，求该单位这次参观世博会的共有几人？
<result>40</result>