The formula for calculating the percent of change between two values over time is:

#p =(N - O)/O * 100#

Where:

#p# is the percent of change - #300%# for this problem

#N# is the New Value - what we must solve for

#O# is the Old Value - #$25# for this problem

Substituting and solving gives:

#300 = (N - 25)/(25) xx 100#

#300 = (N - 25)/color(red)(cancel(color(black)(25))) xx color(red)(cancel(color(black)(100)))4#

#300 = 4(N - 25)#

#300/color(red)(4) = (4(N - 25))/color(red)(4)#

#75 = (color(red)(cancel(color(black)(4)))(N - 25))/cancel(color(red)(4))#

#75 = N - 25#

#75 + color(red)(25) = N - 25 + color(red)(25)#

#100 = N - 0#

#100 = N#

#N = 100#