The bookstore has a promotional activity of "buy 3 and get 1 free". The original price of a storybook is 12 yuan each. If you buy 20 such storybooks at a time, how much will you spend in total?
书店进行"买3本送1本"的促销活动，一种故事书原价每本12元，如果一次买20本这样的故事书，一共只要花多少钱？
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">5 * 1</gadget>
<output>5</output>

<gadget id="calculator">20 - 5</gadget>
<output>15</output>

<gadget id="calculator">15 * 12</gadget>
<output>180</output>

<result>180</result>