Merge Rows Depending on List Criteria

Hi,

Basically In column B I have a list option. If I pick a certain one I want it the spreadsheet to merge a certain amount of cells. Ie 2x. Then Column A row 5 &6 will merge.

If they pick a different option on the list it will merge with a different amount. I.e. 4x+_ then merge with the below 4 rows.

See attachment's for example.