JSFiddle - React, Tailwind, and code Playground

HTML

<form name="oil">Starting amount of oil
    <input type="text" name="start" />Time since oil change
    <input type="text" name="time" />Total amount of oil in car now(quarts)
    <input type="text" name="amount" />
    <input type="submit" />
    <input name="result" readonly="readonly" />
</form>

JavaScript

document.oil.onsubmit = function () {
    var start = document.oil.start.value;
    var lastOilChange = document.oil.time.value;
    var totalOil = document.oil.amount.value;
    if (lastOilChange > 6 || start < totalOil) {
        document.oil.result.value = "you need to change the oil";;
    } else {
        document.oil.result.value = "Everything Is all good";
    }
    return false;
}