pengurangan di php

<?php
$nilai_diterima = 0;
$nilai_pengeluaran = 0;
$hasil = 0;

$x=mysql_query("select sum(total_harga) as total from diterima");
$xx=mysql_fetch_array($x);

$nilai_diterima = $xx['total']; #Memasukkan hasil query diterima ke $nilai_diterima

echo "<b> ". number_format($xx['total']).",-SR</b>";
?>
</td>
</tr>
<tr>
<td>
<td colspan="4">Total Issue</td>
<td>
<?php
$x=mysql_query("select sum(cost_pengeluaran) as total from pengeluaran");
$xx=mysql_fetch_array($x);

$nilai_pengeluaran = $xx['total']; #Memasukkan hasil query pengeluaran ke $nilai_pengeluaran

echo "<b> ". number_format($xx['total']).",-SR</b>";

$hasil = $nilai_diterima - $nilai_pengeluaran; #Hasil pengurangan
echo $hasil; #Cetak Hasil
?>