Xinqiang bought 1 pen and 1 notebook for 3.6 yuan, and Xiang Wei bought the same pen and 4 notebooks for 10.5 yuan. What is the unit price of the pen?
新强买了1枝钢笔和1本笔记本共用3.6元，向伟买了同样的1枝钢笔和4本笔记本共用了10.5元，钢笔的单价是多少元．
<gadget id="calculator">10.5 - 3.6</gadget>
<output>6.9</output>

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

<gadget id="calculator">6.9 / 3</gadget>
<output>2.3</output>

<gadget id="calculator">3.6 - 2.3</gadget>
<output>1.3</output>

<result>1.3</result>