Aggregations query in mongodb

Hello, everyone,

I’m new using mongodb and I would like to understand how can I average this two different arrays inside a document (?)

_id: 662faf78c72912217485c5c5
level1:Object
t level2:Object

t t level3:Value

t t level3
t t t Array (2)

t t t0
t t tArray (62)

t t t1
t t tArray (59)