Automate Goal Seek in VBA??

Dear All

I'm a complete newbie at VBA (the very little I do know is by reading forums and cut/pasting trial/error!). I was wondering if you could help me with the following. I will simplify my question and hope it makes it easier to understand what I am trying to achieve...

I have a workbook with Sheet1 and Sheet2.

When cell A60 in Sheet1 has a value of "a" ("a" means that this cell is selected/activated), I would like to automatically calculate, using Goal Seek, the value of cell M6 in Sheet2 by setting cell H40 (in Sheet2) to a value of 0.00. (I will then link cell M6 in Sheet2 to a cell in Sheet1 to show this value).

(There is a simple calculation in cell H40 which uses inputs from M6, but I'm not sure if it's relevant to post here).

Could anybody suggest a block of code as really I have no idea where to start?

Many thanks