The students planted trees. The senior grades planted 180 trees, 4 more than the middle grades, and the middle grades planted 2 trees less than the lower grades. How many trees did the lower grades plant?
同学们植树，高年级种树180棵，比中年级的2倍多4棵，中年级种的棵数又比低年级的3倍少2棵，低年级种树多少棵？
<gadget id="calculator">180 - 4</gadget>
<output>176</output>

<gadget id="calculator">176 / 2</gadget>
<output>88</output>

<gadget id="calculator">88 + 2</gadget>
<output>90</output>

<gadget id="calculator">90 / 3</gadget>
<output>30</output>

<result>30</result>