function parseCustomValue(customField) {
    var value = parseFloat(workItem.getCustomValue(customField));
    if(!value || value < 0) {
    var value = 0;
    }
    return value;
}

var ubv =  parseCustomValue("userBusinessValue");
var tc = parseCustomValue("timeCriticality");
var rroev = parseCustomValue("rROEnablementValue");
var js = parseCustomValue("initialStoryPoints");

result = (ubv + tc + rroev) / js;

if(!result || result == Infinity)    {
    result = 0;
}

result.toFixed(2);