PHP multiply Two fields

PHP multiply Two fields

I am trying to multiply to fields together to obtain a total in PHP form.
<label for="190_mnth2"></label>
<div align="center">
<input name="190_mnth" type="text" id="190_mnth2" value="10"
size="5" />
</div></td>
<td><div align="center">
<label for="190_rate"></label>
<input name="190_rate" type="text" id="190_rate" value="190.00"
size="10" />
</div></td>
<td><div align="center">
<input name="total_190" type="text" id="total_190" value=<? echo
'190_mnth2' * '190_rate' ?> size="10" />
The above is my current code but the answer is totally wrong it gives me
36100 What is wrong with my formula if anyone can assist?