Simple Online Numerical Calculation Tool With Back-end

We need to create a simple HTML tool that does the following:

INITIAL STEPS - USER INTERFACE

User enters 3 different inputs:

"What is your objective?" has to be chosen from a list which is defined by admin (1)
"What is your overall budget?" - a number in USD
"What is your timeframe?" has a start and end date or number of days option

ALGORITHM AND OUTPUT

Once a user clicks on submit, some mathematical calculations happen in the code:

Calculate the number of days (End Date minus Start Date)
Perform simple mathematical division and multiplication on the number to get Monthly budget

Multiply the monthly budget by rule provided by the admin (2), to give the USD amount for the segment.

Compare that USD amount with the minimum amounts (3), which are also provided by admin. If it is below the minimum in that table, then assign that amount to the cell that has the next highest amount in that same line first, then the next highest amount in another line, until you are above the minimum.

Display those numbers as a "Monthly" budget table (see "Output examples" in the images attached)

Perform simple mathematical calculation on the number in that table to get to the "Overall" table.

Check that the sum matches the initial overall budget

ADMIN INTERFACE

In the password-protected admin section, we should be able to:

Add or remove options from the List of objectives (1)
Create and amend two numerical data tables (2) and (3) to set the budget rules
Add extra entries to the tables, so that we can add more options in the future.