Suguo Supermarket launched a promotional activity during the "May 1st" period. Each notebook is 3.5 yuan, buy two get one free, and the school buys all notebooks for 70 yuan at a time. How many notebooks can you buy?
苏果超市"五•一"期间开展促销活动，每本笔记本3.5元，买二送一，学校用70元一次全部购买笔记本，可买多少本．
<gadget id="calculator">70 / 3.5</gadget>
<output>20</output>

<gadget id="calculator">70 / 3.5 / 2</gadget>
<output>10</output>

<gadget id="calculator">20 + 10</gadget>
<output>30</output>

<result>30</result>