Filter & COUNTIF

Hi, I'm a newbie and was wondering if someone would kindly help me with the following?

In the MHT screen-shot below is a view of a worksheet named: Summary. On this worksheet the use (user has very little experience in Excel 2003) selects an Operation in cell B2 via a drop-down list and a Task Group in cell B4 via a drop-down list.

Any help would be greatly appreciated,

Kind regards,

Chris