There is a pen in a stationery store that used to be 16 yuan per pen, but now it offers "buy 3 pens, get 1 free". How many yuan does Xiaohui need to prepare to buy 4 pens like this.
某文具店有一种钢笔原来每枝16元，现在推出"买3枝送1枝"，小惠买4枝这样的钢笔需要准备多少元人民币．
<gadget id="calculator">16 * 3</gadget>
<output>48</output>

<result>48</result>