The school buys saplings to green the campus, each sapling is 20 yuan, buy 4 and get 1 free, the school buys back a total of 20 saplings, how much is it spent?
学校买树苗绿化校园，每棵树苗20元，买4棵送1棵，学校一共买回20棵树苗，用去多少元钱．
<gadget id="calculator">4 + 1</gadget>
<output>5</output>

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

<gadget id="calculator">20 - 4</gadget>
<output>16</output>

<gadget id="calculator">16 * 20</gadget>
<output>320</output>

<result>320</result>