The third grade needs to water 300 trees, 180 trees have already been watered, and the rest will be watered by 4 groups. How many trees do each group need to water on average?
三年级要浇300棵树，已经浇了180棵，剩下的分给4个组来浇，平均每组要浇多少棵？
<gadget id="calculator">300 - 180</gadget>
<output>120</output>

<gadget id="calculator">120 / 4</gadget>
<output>30</output>

<result>30</result>