Xiaohong's father gave her 3 yuan to buy books, and 3 yuan to buy 6 exercise books. When buying books, she found that the money for buying books was not enough, so she had to take part of the money for buying exercise books. In this way, she only bought 4 exercise books. How much did she spend on buying the books this time?
小红的父亲给她3元去买书，3元买6本练习本，买书时她发现买书的钱不够，只好从买练习本的钱中拿出一部分后才够．这样，她只买了4本练习本，这次买书花了多少钱？
<gadget id="calculator">3 / 6</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">6 - 4</gadget>
<output>2</output>

<gadget id="calculator">(1/2) * 2</gadget>
<output>1</output>

<gadget id="calculator">1 + 3</gadget>
<output>4</output>

<result>4</result>