how can I use the results of one program in another program

Hi all:

I am a new user of Stata programming and I met some difficulty in ado file programming.

I have written an ado-file, which I want to use repetitively in later programming process. I return some of the values in this ado file but I have no idea how to retrieve this value in another program. For example,
program prog1

return p75 = r(p75)
return p25 = r(p25)
end
Then how can I use the scalar p75 in another program?
For example,
program prog2

scalar a = p75 + p25

end

Thank you so much!!!