The students went out to plant trees. There are 56 girls and 28 boys. Every 4 people are divided into groups. How many groups can they be divided into?
同学们外出植树．女生56人，男生28人，每4人分成一组，可以分成多少组？
<gadget id="calculator">56 + 28</gadget>
<output>84</output>

<gadget id="calculator">84 / 4</gadget>
<output>21</output>

<result>21</result>