A storybook is 7 yuan, a technology book is 12 yuan, Xiaodong bought 3 storybooks and 3 science books each, how much did he pay in total?
一本故事书7元，一本科技书12元，小东故事书和科技书各买了3本，他一共付了多少元？
<gadget id="calculator">12 + 7</gadget>
<output>19</output>

<gadget id="calculator">19 * 3</gadget>
<output>57</output>

<result>57</result>