Using FILTER with SUMX & DISTINCT

Hi

I have two tables -

1) A student information table (Master Table) stating if they were admitted or denied for a course. For those admitted, I have a column calculating revenue earned from that student (for denied students it return $0). The table also indicates name of the event students attended and learned about the course.

2) An events table (Event Category) with names of each event and cost associated with the event. 

I want to calculate ROI for each event. I used the following formula.

ROI = DIVIDE([Returns],SUMX(DISTINCT('Event Details'[Event Category (City)]),Master[Avg Cost]),0)

Where,

Returns = SUMX(DISTINCT(Master[Revenue]),Master[Revenue])-SUMX(DISTINCT('Event Details'[Event Category (City)]),Master[Avg Cost])

I used the sumx and distinct function as I wanted to sum each row for admitted students returning cost against specific events. e.g. if you consider the following scenario, I want sum of cost associated with Event A, Event B and Event C where Event A's cost is calculated only once. 

Student A Admitted Event A 

Student B Admitted Event B

Student C Denied    Event A

Student D Admitted Event C

The SUMX and DISTINCT function does that for me, however I want to put a filter in the formula so that the measure calculates the returns only for Admitted students.

Can you help me figure this out? I tried using FILTER but it does not work. 

I guess the first question I would have is "why"? If denied students are $0 then including them in a SUM would not affect the result.