<?php
$total = 4000;
$pctm = 30.00;
$valor_descontado = $total - ($total / 100 * $pctm);
echo $valor_descontado;
//https://pt.stackoverflow.com/q/88177/101
PD9waHAKJHRvdGFsID0gNDAwMDsKJHBjdG0gPSAzMC4wMDsKJHZhbG9yX2Rlc2NvbnRhZG8gPSAkdG90YWwgLSAoJHRvdGFsIC8gMTAwICogJHBjdG0pOwplY2hvICR2YWxvcl9kZXNjb250YWRvOwoKLy9odHRwczovL3B0LnN0YWNrb3ZlcmZsb3cuY29tL3EvODgxNzcvMTAx