Macro code to insert 3 rows on spreadsheet with variable number of rows

I have a need to include the macro code to insert three blank rows on the 2nd to last row
"and" add text in cell columns C & D associated with the added rows. If the existing file
has 13 columns, the new file would have 13 rows. I can't overwrite the last row information
as I am trying to just push it down 3 rows.

The spreadsheet the macro calls up is an existing spreadsheet data base file and the existing number of rows will have to be determined.
All the columns have the same number of rows and the last row is sum of the columns. I'm trying to insert 3 new rows above the
above the last row and also "hard code" text in the Columns C and D associated with the new rows.

For help purposes the sample text could be
"text C1" .. located on the 1st new inserted row & 2th Column (Col C) "text D1" .. located 1st new row column D
"text C2" .. located on the 2nd new inserted row and 4th Column (Col D) "text D2" .. located 2nd new row column D
"text C3" .. located at the 3rd new inserted row and 4th Column (Col D) "text D3" .. located 3rd new row column D

Thanks in advance for any suggestions or help.