<?php
$vardim = array("ahmet", "ahmet 2", "derya", "esma", "selim", "ahmet 3");
$count = 0;

foreach($vardim as $item) {
    if (strpos($item, "ahmet") !== false) {
        $count++;
    }
}

echo "Toplam " . $count . " adet ahmet bulundu.";
?>