db={"tour":[{"_id":ObjectId("622385ab1b68d9136e48ba51"),"source":"Pune","destination":"Kashmir"},{"_id":ObjectId("622385ba1b68d9136e48ba52"),"source":"Mumbai","destination":"Shilong"},{"_id":ObjectId("622385ce1b68d9136e48ba53"),"source":"Nashik","destination":"Goa"}],"turism_ind":[{"_id":ObjectId("6223885d1b68d9136e48ba57"),"ind_name":"Veena World","package":[{"pkg_id":111,"tour_id":ObjectId("622385ba1b68d9136e48ba52"),"cost":85000}],"cust_review":[{"cust_id":ObjectId("622387fa1b68d9136e48ba56"),"rating":4}]},{"_id":ObjectId("622389191b68d9136e48ba58"),"ind_name":"GK Travels","package":[{"pkg_id":222,"tour_id":ObjectId("622385ba1b68d9136e48ba52"),"cost":82000},{"pkg_id":223,"tour_id":ObjectId("622385ab1b68d9136e48ba51"),"cost":78000}],"cust_review":[{"cust_id":ObjectId("622387f51b68d9136e48ba55"),"rating":5}]},{"_id":ObjectId("622389ae1b68d9136e48ba59"),"ind_name":"KK Tours","package":[{"pkg_id":333,"tour_id":ObjectId("622385ce1b68d9136e48ba53"),"cost":57000},{"pkg_id":334,"tour_id":ObjectId("622385ab1b68d9136e48ba51"),"cost":79000}],"cust_review":[{"cust_id":ObjectId("622387f51b68d9136e48ba55"),"rating":5},{"cust_id":ObjectId("622387ef1b68d9136e48ba54"),"rating":4}]}],"customer":[{"_id":ObjectId("622387ef1b68d9136e48ba54"),"cust_name":"Aniket","selected_pkg":[111]},{"_id":ObjectId("622387f51b68d9136e48ba55"),"cust_name":"Nik","selected_pkg":[222,333,334]},{"_id":ObjectId("622387fa1b68d9136e48ba56"),"cust_name":"Sham","selected_pkg":[111,222]},{"_id":ObjectId("62238c671b68d9136e48ba5a"),"cust_name":"John","selected_pkg":[111,222,223,333,334]}],}

db.customer.aggregate([{"$match":{"cust_name":"John"}},{"$project":{"firstThree":{"$slice":["$selected_pkg",0,3]}}},{"$lookup":{"from":"turism_ind","localField":"firstThree","foreignField":"package.pkg_id","as":"tour"}},{"$project":{"_id":0,"packages":{$reduce:{input:"$tour.package",initialValue:[],in:{$concatArrays:["$$value","$$this"]}}}}},{"$project":{"packages":1,"total":{"$sum":"$packages.cost"}}}])