Get value with JQuery in gravity form

I'm trying to add a formula to my gravity form (WordPress) which includes exponent.i cant use the build in calculator since there is no exponent function. its basically a loan calculator where.

r=rate ;(form_id=4)/12

p=loan amount ;(form_id=1)

D=duration ;(form_id=2, [drop down menu]) * 12

X=p(r/1-(1+r)^-D)

X= repayment

Now I get the r, p and D from the form in form of drop down and written numbers.

so far I've put a HTML box and inserted this code in it :

<script>
gform.addFilter( 'gform_calculation_result', function(result, formulaField, formId, calcObj ){    
if ( formulaField.field_id == "2" ) {
    result = /****/;
}
return result;
});
</script>

I don't have any programming bg and I got it from a support team member.

What I understand is that this code will replace the calculation of field_id 2 (which is showing the X=[monthly repayment] with the result of my formula -> "/****/"

But i have to write the formula and i don't know how to get the values from the form with jQuery and put them in the formula.

I found out JavaScript math functions from W3school and another website so i don't have problem with writing the formula i just need help with jQuery to get the value.

I was wondering if someone can help me with that?

You can grab the field values using jQuery .val(). So if you wanted to get the value for field 5 you could use something like this

var field_five = jQuery('#input_2_5').val();

Input id's follow the naming convention of input_{form_id}_{field_id} and for multi input fields they will end with _{input_no}. You can confirm what the input id is by inspecting the field using the browsers developer tools where you would see something like this.

<li id="field_2_5" class="gfield">
    <label class="gfield_label" for="input_2_5">Number</label>
    <div class="ginput_container">
        <input name="input_5" id="input_2_5" type="text" value="" class="medium" tabindex="5">
    </div>
</li>

To use the retrieved value in the calculation the script would look like this:

<script>
gform.addFilter( 'gform_calculation_result', function(result, formulaField, formId, calcObj ){    
    if ( formulaField.field_id == "2" ) {
        var field_five = jQuery('#input_2_5').val();
        result = field_five * 12;
    }
    return result;
});
</script>