<INPUT TYPE="text" NAME="count" value =2>
<INPUT TYPE="text" NAME="cost" value =3>
<INPUT TYPE="text" NAME="sum" onclick= "this.value=eval(count.value*cost.value)">
<INPUT TYPE="text" NAME="cost" value =3>
<INPUT TYPE="text" NAME="sum" onclick= "this.value=eval(count.value*cost.value)">
function getSum() {
sum.value = count.value * cost.value;
}
</script>
<INPUT TYPE="text" NAME="count" value =2>
<INPUT TYPE="text" NAME="cost" value =3 onblur="getSum()">
<INPUT TYPE="text" NAME="sum">
<INPUT TYPE="text" NAME="cost" value =3 onkeydown ="if(event.keyCode==13){sum.value= count.value*this.value}">
<INPUT TYPE="text" NAME="sum" onclick= "">