The unit price of a pen is 3.5 times the unit price of a ballpoint pen. The teacher bought a pen and 5 ballpoint pens as prizes, and the total cost is 8.5 yuan. Find the unit price of the ballpoint pen.
一支钢笔单价是一支圆珠笔单价的3.5倍，老师买了一支钢笔和5支圆珠笔做奖品，一共用去8.5元，求圆珠笔的单价．
<gadget id="calculator">5 + 3.5</gadget>
<output>8.5</output>

<gadget id="calculator">8.5 / 8.5</gadget>
<output>1</output>

<result>1</result>