this helped, I've asked a friend who's created this, just thought I'd add it in case anyone else wondered
function WO() {
var tbody = document.getElementById("plateVolumes");
for(var i = 0; i < tbody.rows.length; i++) {
var row = tbody.rows[i];
var qty = row.cells[1].childNodes[0].value;
var price = row.cells[3].childNodes[0].value;
var answer = (Number(qty) * Number(price)).toFixed(2);
row.cells[4].childNodes[0].value = answer;
}
}