Mortgage Calculator Form Creation

Hi,
We need to build two mortgage calculators with Gravity form or some other solutions.
The user will submit a form with minimal information (First name, last name, phone, email, address) and will receive the answer by email.
We have already some licenses to perform it:
- Cost Calculator by stylemixThemes : https://stylemixthemes.com/cost-calculator-plugin/templates/simple-mortgage-calculator-template/
- Gravity Math: https://www.gravitykit.com/gravity-forms-mortgage-calculator/
- Or a solution you will suggest.
There are two forms, and we have the following math formulas:
First Form Mortgage: visitor provide the amount of the credit
Monthly fee = ( Amount of the credit * TB ) / ( 1 - ( 1 / ( 1+ TB ) ^ duration ))
( round to the second decimal place )
Note:
TB = monthly rate who will depend on the available list of monthly rates and depend on the duration of the credit AND if the credit is fixed of variable: a list of available duration and for each duration the % who needs to be applied.
Examples:
Fixed 10 years : 3.20%
Fixed 15 years : 3.20%
Fixed 20 years : 3.20%
Fixed 25 years : 3.20%
Variable 10 years : 3.32%
Variable 15 years : 3.34%
Variable 20 years : 3.36%
Variable 25 years : 3.36%
Second Form Mortgage:
Same Formula but instead of providing the amount of credit the visitor will provide the Monthly fee he would like to pay.
We have our old system running here: https://www.segersassocies.be/simulation-credit-hypothecaire.php