Field numerical change based on other field.

Hi There,

I was wondering if anyone could help me generate a code for a problem I have in Acrobat. I have two fields, one which will have a user entered number and another which will display a different number based on the user input. 

For example: The user inputs (16) into their field and the second field would populate (3). Likewise, if the user inputted (8) the second field would display (-1).

This was this code I've been working on but I cannot seem to get it right. Any thoughts?

switch(event.value) {

case "SCORE":

var nSubTotal = this.getField("subtotal").value;
if( nSubTotal > 28 ) event.value = 9;
else if( nSubTotal > 26 ) event.value = 8;
else if( nSubTotal > 24 ) event.value = 7;
else if( nSubTotal > 22 ) event.value = 6;
else if( nSubTotal > 20 ) event.value = 5;
else if( nSubTotal > 18 ) event.value = 4;
else if( nSubTotal > 16 ) event.value = 3;
else if( nSubTotal > 14 ) event.value = 2;
else if( nSubTotal > 12 ) event.value = 1;
else if( nSubTotal > 10 ) event.value = 0;
else if( nSubTotal > 8 ) event.value = -1;
else if( nSubTotal > 6 ) event.value = -2;
else if( nSubTotal > 4 ) event.value = -3;
else if( nSubTotal > 2 ) event.value = -4;

}