如何在MongoDB查询中访问子文档?

So I have the following code. I need it to run in the MongoDB shell. It queries the database for people with their attribute marked as true. Now I am having trouble because I do not know how to change the numcollect portion of my query into an array. I am trying to average all the numbers in the numcollect collection. I know this code is incorrect but it shows what I'm trying to do. What do I need to change?So I have the following code. I need it to run