There are 180 students in the third and fourth grades, including 87 students in the third grade. How many students are there in the third grade than in the fourth grade?
三、四年级共有学生180人，其中三年级有87人，三年级比四年级少多少人？
<gadget id="calculator">180 - 87</gadget>
<output>93</output>

<gadget id="calculator">93 - 87</gadget>
<output>6</output>

<result>6</result>