The children's bookstore brings in 15 kinds of storybooks, 30 of each kind. After selling some, there are 120 left. How many storybooks are sold?
少儿书店运进15种故事书，每种30本，卖出一些后，还剩120本，卖出多少本故事书？
<gadget id="calculator">15 * 30</gadget>
<output>450</output>

<gadget id="calculator">450 - 120</gadget>
<output>330</output>

<result>330</result>