Set Analysis to Calculate Avg Days a Lead in Each Stage

[kishoreravi1983]

Hi All,

Can you please help me to write a set Expression to calculate a Avg days spent  a lead in each stages

These are stages a Lead passes into :  We have new value and old value of each lead

I want to create a Staked Bar Chart. Month has Dimension and Stages 

Attached the Data set

Propose
Qualify
Negotiate
Develop
Closing Signed Won