javascript code for multiply two field

I want to multiply two field as below:

function multiply()

{
var val1 = Xrm.Page.getAttribute(‘new_tax′).getValue();
var val2 = Xrm.Page.getAttribute(‘baseamount′).getValue();

if(val1==null)return;
if(val2==null)return;

var result = val1*val2;
Xrm.Page.getAttribute(‘tax’).setValue(result);
}

unfortunately I meet an error

'multiply' is undefined.