With the money that Xiaohong brings, if she buys a book worth 2.4 yuan, she will have 2.1 yuan left; if she buys two ballpoint pens instead, she will have 1.3 yuan left. How much is each ballpoint pen?
小红所带的钱，如果买一本2.4元的书，可剩下2.1元；如果改买2支圆珠笔，可剩下1.3元．每支圆珠笔多少元？
<gadget id="calculator">2.1 - 1.3</gadget>
<output>0.8</output>

<gadget id="calculator">2.4 + 0.8</gadget>
<output>3.2</output>

<gadget id="calculator">3.2 / 2</gadget>
<output>1.6</output>

<result>1.6</result>