Hi,
Frequency is related to time using the formula : F = 1 / T, where F is the frequency in Hertz and T, the time in seconds. Now, if you want to generate a new clock with a period of 25 mSec, then
F = 1 / T => 1 / 25mSec => 0.04 Khz or 40 Hz; a dramatic decrease in frequency from your source clock 96 Mhz. What you're asking for is the decreasing factor that will decrease the 96 Mhz clock to a new clock of 40 Hz. Simply use :
Ratio : 96E6 Hz / 40 Hz = 2400000. So, the 96 Mhz has to be decreased by a ratio of 2400000 in order to get a new clock of 40 Hz. A rather annusual decrease factor.
Hope it'll help.