Calculate Relative %

[qlikviewaf]

Hi!

i have as dimension Item_Number - and an expression sum(Quantity).

I would like to create an additional expression, that shows the relative % of each item number (based on the selection done on item number). 

Example, here below i selected just 8 different item number - i would like to get the % relative for each item in temrs of quantity.

How can be done ?
Thanks!!

i would like to calculate the column % 

[Or]

Sum(Quantity) / Sum(total Quantity), perhaps? Not sure if there's any other factors at play here which might require modifying that.