Attempting to use checkbox in adobe using java Script to reset the values of fields and add in another

I am trying to figure out how to get a checkbox in adobe using javascript to change the values from current value of multiple fields if checked to 0 and another field to change the value to 85

    var FX1 = Number(this.getField("RegistrationFee").valueAsString);
    var FX2 = Number(this.getField("TitleFee").valueAsString);
    var FX3 = Number(this.getField("LienFee").valueAsString);
    var FX4 = Number(this.getField("CountyFee").valueAsString);
    var FX5 = Number(this.getField("TransferFee").valueAsString);
    var FX6 = Number(this.getField("TagFee").valueAsString);
    
    if (this.getField("OutOfState").value != "Off") {
    event.value(FX1,FX2,FX3,FX4,FX5) = 0;
event.value = (FX6 = 0, +85)}

kinda gave up on last part, im still new to coding and would appreciate the help!