[{"projects":[{"_id":"609d1a10b588c73aeee9aac9","projectType":"public","status":"completed","amt_paid":100,"revisionStatus":false,"commission":20,"engineer_submission":"true","revenueOnRevision":10},{"_id":"609d3754b588c73aeee9aae8","projectType":"public","status":"open","amt_paid":50,"totalBids":0,"revisionStatus":false,"commission":30,"engineer_submission":"false","revenueOnRevision":100}]}]

db.collection.aggregate([{$set:{totalAmt:{$sum:{$concatArrays:["$projects.amt_paid","$projects.commission","$projects.revenueOnRevision"]}}}}])