I want to perform a calculation on a range of dates as follows

Date 1 - 2-7-07
Date 2 - 8-7-07
Date 3 - 2-7-08
Date 4 - 8-7-08

For output 1 I would like to multiply 5*(date2-date1)
For output 2 I would like to multiply 5*(date3-date2)
For output 3 I would like to multiply 5*(date4-date3)

and then store those values... multiply each of the outputs as FINAL1.

Then step down one step and have:
For output 2b I would like to multiply 5*(date3-date2)
For output 3b I would like to multiply 5*(date4-date3)

and then store those values... multiply each of the outputs as FINAL2.

simple if my number of dates doesn't change, but what if I have ten dates
one time and 3 the next? How can I get a variable number of outputs/Finals?

THANKS SO MUCH!