How to solve these type of questions

[Sreeja06]

Hello, how to implement and check answer for following question

You have three program statuses in your Email Send channel, in this order and with this amount of leads at each stage:
Sent (Step 10): 10 members /
Opened (Step 20): 10 members /
Clicked (Step 30 - Success): 15 members.
Based on this setup, the total number of people who opened this email is 10.
How many are the total members in the program?
10
20
30
35

[SanfordWhiteman]

Don’t know what you mean by “implement” but Program Member Status is mutually exclusive. Therefore the answer is 35: the statuses do not overlap.

[Sreeja06]

How to verify that member status do not overlap ?