Problem Statement

CSV spreadsheet files are suitable for storing tabular data in a relatively portable way. The CSV format is flexible but somewhat ill-defined.
For present purposes, authors may assume that the data fields contain no commas, backslashes, or quotation marks.

Read a CSV file, change some values and save the changes back to a file. For this task we will use the following CSV file: Suggestions

Let's start with the solution:

import delim input.csv, clear 
replace c5=c3+c4
egen sum=rowtotal(c*)
drop if mod(c3,3)==0
export delim output.csv, replace