operation with series

[elmismo999]

Hello,
if I have 2 series:

Serie1
Name Number
---- ------
a 10
b 20
c 30
Serie2
Name Number
---- ------
a 5
b 30
c 100

I would like to have a result serie with the following condition :
1) Just positve Diff between Serie2 - Serie1
2) Order the result desc

Result
Name Number
---- ------
c 70
b 10

Thank You -