Hi Does anyone know what i'm doing wrong here. Instead of adding my numbers together its putting them next to each other?

This is the javascript...

Code:
<SCRIPT LANGUAGE="JavaScript">

<!--
var myIncome1;
var myIncome2;
var myIncome3;
var myIncome4;


function HowMany(form)
{
var totalincome;
totalincome = (myIncome1 + myIncome2 + myIncome3 + myIncome4);
form.Tincome.value = totalincome;
}

function SetMyIncome1(inc1)
{
myIncome1 = inc1.value;
}

function SetMyIncome2(inc2)
{
myIncome2 = inc2.value;
}

function SetMyIncome3(inc3)
{
myIncome3 = inc3.value;
}

function SetMyIncome4(inc4)
{
myIncome4 = inc4.value;
}

function ClearForm(form){

form.myIncome1.value = "";
form.myIncome2.value = "";
form.myIncome3.value = "";
form.myIncome4.value = "";
form.Tincome.value = "";


}


// -->

</SCRIPT>
This is the form...

Code:
<div><form method="Post">
<div><p>Monthly income</p></div>
<div><p>Pay <input name="myIncome1" type="text" ONCHANGE="SetMyIncome1(this)"/></p>
<p>Benefits <input name="myIncome2" type="text" ONCHANGE="SetMyIncome2(this)"/></p>
<p>Pension <input name="myIncome3" type="text" ONCHANGE="SetMyIncome3(this)"/></p>
<p>Other income <input name="myIncome4" type="text" ONCHANGE="SetMyIncome4(this)"/></p>
<p><INPUT TYPE=BUTTON ONCLICK="HowMany(this.form)" VALUE="Calculate Income"><INPUT TYPE=BUTTON VALUE=" Reset " onClick="ClearForm(this.form)"></p>


<p>Total <input name="Tincome" type="text" value="" /></p></div></form