How can I calculate how long something takes on MS Excel?

I am trying to find out how long it takes to perform a task and using excel to do so. I can do it simply given a standard 5cm/y but to do it properly I need to use 5cm/y for the first year, 2.5cm/y for the the following 5 years, 1cm/y for the following 10 years then 0.5cm/y for every year after that. I am trying to find how many years it takes given a number of centimetres in excel. Anyone know how to do this?
Asked Jul 21, 2013

TIP: If it's not your answer to this question, please click "Leave a Comment" button under the question to communicate with the question owner.