Time Spent for resolved issue in sprint

measures.avg effort to elapsed ratio:

([Measures].[Average hours spent of resolved issues]/8)/([Measures].[average resolution workdays])

where:

average hours spent of resolved issues:

CASE WHEN [Measures].[Issues with Hours spent resolved] > 0
THEN
[Measures].[Hours spent resolved] /
[Measures].[Issues with Hours spent resolved]
END

the point is: 1. how can I roll it up to epic level?
and 2. Time spent in done issues in Epic