The unit price ratio of ballpoint pens and pencils is 4:3, 20 ballpoint pens and 21 pencils total 71.5 yuan. What is the unit price of a ballpoint pen?
圆珠笔和铅笔的单价比是4：3，20支圆珠笔和21支铅笔共71.5元．圆珠笔的单价是多少？
<gadget id="calculator">4 * 20</gadget>
<output>80</output>

<gadget id="calculator">3 * 21</gadget>
<output>63</output>

<gadget id="calculator">80 + 63</gadget>
<output>143</output>

<gadget id="calculator">71.5 / 143</gadget>
<output>0.5</output>

<gadget id="calculator">0.5 * 4</gadget>
<output>2</output>

<result>2</result>