<?php
$myArray = array(
    "0x40x40" => 64, "0x50x40" => 65, "0x60x40" => 66, "0x70x40" => 67, "0x80x40" => 68, "0x90x40" => 70, "0x100x40" => 71, "0x110x40" => 74, "0x120x40" => 76);

echo min($myArray);

64