need help w/code

Hi, will someone tell me the correct way to clear these fields.
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php code;
$zero=0;
// if over-payment subtract over-payment from prevbal field and clear misc chgs
else ($rentpaid > $rentdue )
{ $rentdue = $rentpaid – $rentdue. $prevbal = $zero. $latechg = $zero.
$secdep = $zero. $damage = $zero. $courtcost = $zero. $nsf = $zero. }