Hi @alchan ,
If my understanding is correct your looking for Page Views/Unique Visitors for the visitors who saw page type called "TXT." anytime in their browsing history. If this is correct then you can build this metric by creating a visitor based segment with condition of page type = "TXT." and use this segment in a calculated metric that performs Page Views/Unique Visitors calculation,
Segment:

Calculated Metric:

Please note that above segment will return all the page view across all pages from the visitors who have viewed page type "TXT.". So the calculation in metric give you average page views across all pages from these visitors. If you only want to calculate average page views for pages under page type "TXT." then you can change the segment container from visitor to hit and it should give you the desired data.
Cheers!