The salesperson mistakenly sold a pen with a unit price of 6.4 yuan as 4.6 yuan, and the result was a total of 45 yuan less. How many pens of this kind did he sell in total?
营业员误将单价6.4元一支的钢笔当作4.6元出售，结果共少收45元．他一共卖了这种钢笔多少支．
<gadget id="calculator">6.4 - 4.6</gadget>
<output>1.8</output>

<gadget id="calculator">45 / 1.8</gadget>
<output>25</output>

<result>25</result>