请问为啥我的数学成绩比英语成绩高多少，显示不出啦呢？
<?php
$english = 110; //英语成绩
$math= 118; //数学成绩
$biological = 80; //生物成绩
$physical = 90; //物理成绩
$sum = $english+$math+$biological+$physical;
$avg = $sum/4;
$X = $math - $english;
$x2 = $english * $english;
echo "总分:".$sum."<br />";
echo "平均分:".$avg."<br />";
echo "数学比英语高的分数:".$x."<br />";
echo "英语成绩的平方:".$x2."<br />";
