Mom took 30 yuan to buy stationery for Liu Ning. She first bought 10 exercise books at 1.5 yuan each, and then used the remaining money to buy carbon pens at 2.5 yuan each. Mom can also buy a few carbon pens Pen?
妈妈拿了30元钱为刘宁买文具，她先买了每本1.5元的练习本10本，再用剩下的钱买2.5元一支的碳素笔，妈妈还可以买几支碳素笔？
<gadget id="calculator">1.5 * 10</gadget>
<output>15</output>

<gadget id="calculator">30 - 15</gadget>
<output>15</output>

<gadget id="calculator">15 / 2.5</gadget>
<output>6</output>

<result>6</result>