function mnu1(elem1) {

var rt = elem1.id;
var tt;
tt = rt.replace("b", "a");
document.getElementById(tt).src = "img/" + tt + "s.jpg"
}

function mnu2(elem2) {

var bb = elem2.id;
var ff;
ff = bb.replace("b", "a");
document.getElementById(ff).src = "img/" + ff + ".jpg";


}