Create a complex mathmatical calculation

I need someone to create 3 'Gravity forms' calculators similar to these
https://www.batterystuff.com/kb/tools/calculator-for-load-specific-run-time.html
https://www.batterystuff.com/kb/tools/calculator-sizing-a-battery-to-a-load.html
https://www.batterystuff.com/kb/tools/dc-to-ac-amperage-conversion-run-through-an-inverter.html

The maths can be viewed here https://www.batterystuff.com/kb/tools/math-behind-the-magic.html

This will be the first of several calculators, I also need some charts creating from a Gravity form, so if you have experience in this area, please mention it when bidding.

PLEASE - Do not bid if you are not totally confident & competent.