Solve 2 equations with 2 unknowns in PHP

solve.php

<?php

/**
 * Solves the following equations:
 *
 * a·x + b·y = c
 * d·x + e·y = f
 *
 * Returns an array with [x, y]
 */
function solve($a, $b, $c, $d, $e, $f)
{
  $x = $c * $e - $b * $f;
  $y = $a * $f - $c * $d;
  $z = $a * $e - $b * $d;

  return [$x / $z, $y / $z];
}