function showId(id) {
    if (e=document.getElementById(id))
        e.style.display = "block";
}


function hideId(id) {
    if (e=document.getElementById(id))
        e.style.display = "none";
}

function changeClass(id, toClass) {
    
    if (e=document.getElementById(id)) {
        e.className = toClass;
    }
}




function gasEst() {
    if ((dist=document.getElementById("distance")) && (milesPerGallon=document.getElementById("mpg")) && (dollarsPerGallon=document.getElementById("dpg")) && (est=document.getElementById("estimate"))) {
        temp = "$" + (dist.value * dollarsPerGallon.value / milesPerGallon.value).toFixed(2);
        est.value = temp;
    }
}