Answer: There are 9 people who completed the registration.
Step-by-step explanation:
Since we have given that
Number of emails you send out = 9000
Percent of email are opened = 5%
Number of emails are opened is given by

Out of opened email,
Percent of email click on a link to register for something = 10%
Number of emails are clicked to register is given by

Out of those who clicked the link ,
Percent of people complete the registration = 20%
Number of people who are registered is given by

Hence, there are 9 people who completed the registration.