Value of Measure against previous period

Hi,

*I am a newbie, so it is very much possible that this is a silly/easy question*

I have a table that shows gives me students enrolments into courses . There is a enrolment date as well.

I have added a measure Number of Enrolments = countA('Student Enrolments'[UserName]).

If I add a slicer with Enrolment Date, I can pick the year for which I need the enrolment count. I am stuck on the following requirement.

If I pick a year to get the count of enrolments for the year I need to get the growth % with respect to last year. 

Example, if I pick year 2016 in the time slicer, I should get the following.

Year-Selected Previous-Yr Growth %

120              100                   20

Thanks,

Ninu