In order to know how much time will David and Armando take, you need to write down the given and solve them with the given solution.
David – 15 reports
Armando – 37 reports
Total Reports = 52 reports in total
Total Reports in an hour = 52
Overall total reports = 400
Time to finish = ?
If you try to evaluate, if you have 50 reports in an hour with a total of 400 reports, you could have gain 8 hours by doing the reports.
So to expand more, 52 reports will be divided into 400, giving a total of 7.6
So the answer is that they will take 7 hours and a half in doing the reports.