Joining 3 Tables

Screen Link:

My Code:

SELECT track.track_id, AS track_name, AS track_type, invoice_line.unit_price, SUM(invoice_line.quantity)
FROM track 
INNER JOIN invoice_line ON invoice_line.track_id = track.track_id
INNER JOIN media_type ON media_type.media_type_id = track.media_type_id
WHERE invoice_id = 4;

What I expected to happen:
I expected this code to work since I followed the syntax per the lesson. However, when I checked the answer I realized that the answer query actually uses media_type as the first table to join rather than track. Why?

What actually happened:

The value for result doesn't look right.

Yeah, basically what I asked above. Also, a question I have is, how would I verify that my answer is correct or not in a real life setting for a problem like this, for example? Thanks! invoice_line.quantity already contains the quantity needed, so there is no need to use the aggregate function SUM().