Xinhua Bookstore sells each set of story books for 42 yuan, and if you buy 6 sets, you will get one free. Teacher Li bought 6 sets of story books for the school at one time. How much is each set cheaper?
新华书店每套故事书卖42元，如果买6套送一套．李老师为学校一次性买了6套故事书，每套便宜多少钱？
<gadget id="calculator">6 / 7</gadget>
<output>6/7 = around 0.857143</output>

<gadget id="calculator">42 * (6/7)</gadget>
<output>36</output>

<gadget id="calculator">42 - 36</gadget>
<output>6</output>

<result>6</result>