[Diphenyl Oxalate]

nikoshot,

var a = document.getElementById("metr"),
    b = document.getElementsByName("radio-531"),
    c = document.getElementById("summ");

b[0].onchange = b[1].onchange = a.onkeyup = function () {
	c.value = a.value * (b[0].checked ? 90 : 40);
};