Xiaowen and his 3 good friends went to buy books, each of them bought 3 books, and the price of each book was 3 yuan, how much did they spend in total?
小文和他的3个好朋友去买书，每人买了3本，每本书的价钱都是3元，他们一共用去多少元？
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<gadget id="calculator">3 * 3 * 4</gadget>
<output>36</output>

<result>36</result>