Copy the 2011 dates to another sheet? Auto filter the range with custom filter options: greater than and equal to 1/1/2011 and less than and equal to 31/12/2011 (enter dates in the format according to your regional settings).
The bottom left hand corner of the screen will show you how many...
The code goes into the worksheet change event procedure. In the VBA editor's Project Explorer window, double click the sheet name which has the cells you want to monitor. Then paste the following code. Assuming your 'Solve' macro is currently in a module, this should work:
Option Explicit...