Adjustable price calculation form

i need to solve following business requirement:

User gets a monthly premium (price in $) proposal based on his input of:

  • Term (for how long will be paying monthly premium - in years)
  • Sum assured (insured sum - in thousands of $ )

Monthly premium is higher if he enters higher premium and term. We need to give him option to "play" and recalculate offer:

  • by changing monthly premium that he needs to pay by recalculating sum assured and term
  • by changing sum assured that he needs to insure by changing monthly premium and term

Some basic sketches are here:

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My Questions are:

  • Are there some examples of design patterns for this problem?
  • Does someone have more elegant idea to solve this one?
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