VBA Code That Will Sum 30 Columns Within A Row

Is there a way to write a macro that will insert a column into another workbook at column C, then put a formula into every row of that column (down to the last row) that will basically be the equivalent of "sum the thirty columns to the right within this row"

What I need to happen next, is that the code repeat this process of summing 30 cells to the right, (or inserting a formula that will) all the way down to the last row. Then copy that data, paste it into Column H of the workbook containing the macro. Then close the other workbook without saving the changes.

I can't simply do something like, =sum(D6:AH6) ,because another department keeps inserting a new column in front of column E every day. So, if the ending column is locked on a particular cell, the sum range will grow by 6 every week. I simply need to get the sum of D6 and the next 30 columns to the right of it.

The code I'm requesting should sum the 30 columns to the right of column D (beginning at the 6th row, then down to the last row), or insert a formula that will do this, and drag the formula down. This action will be done in another workbook.