Simple Php program that accumulates total of an activity over time

Need a simple php app that calculates time and cost of an activity over various timespans (ie. months, year, etc... ).

Then it'll calculate how much time is saved if an activity's time is reduced by a certain percentage.

Coding should be structured and modular, possibly object oriented and use standard naming conventions.

Right now the focus is on programming without hard coding to text fields.
To test the program create simple text fields on html page. Also returns answers to text fields on same page.

Feel free to ask questions you have. Please send your time and cost estimate.

The work is programming for hire. And I retain and gain rights to all work done.

You must be willing to answer questions about your work. And get the app installed and working on my website.

I've created a few method-names and method signatures that'll make it modular.

Can you add a debug_flag that, if turned on, writes requests and parameters to a log?

PHP 5.5.30

This quick job is just the start. Another job will retrieve starting data and save
save it to a database.

If interested then leave your time and cost estimate.