ver .4n
gin .6n

add is x ounces of gin

ver .4n
gin .6n + x

hence equations becomes

.4n / (n+x) = .25
solve it and you will get x = 3n/5

or the other equation will be
(.6n + x) / (n+x) = .75
solve it and you will get x = 3n/5


You can also solve this by sample values
lets say total vol = 100 (=n)
ver = 40
gin = 60

now we want 40 to become 25%
that means total has to be 160
so we need to add 60 ounces of gin

60 is actually 3/5 of 100
so ans