Xiao Zhang organizes several friends to buy tennis rackets online. No matter how many rackets are purchased, the total postage of the seller is 60 yuan. Before Xiao Zhang placed the order, a friend called to say that he wanted to buy 5 more rackets, which reduced the original postage for each racket by 2 yuan. Then how many rackets are bought in total in this group purchase.
小张组织几个朋友在网上一起购买网球拍，不论购买几个球拍，卖家发货的总邮费都是60元．在小张下订单前，有朋友打电话来说要多买5个，这使原来每个球拍平摊的邮费又少了2元．则这次团购共买球拍多少个．
<gadget id="calculator">10 + 5</gadget>
<output>15</output>

<result>15</result>