Teacher Xiao wants to buy 50 footballs for the school. There are two stores to choose from. The price of footballs in the two stores is 50 yuan, but the preferential methods of each store are different. Store A: buy 10 and get 2 free, if less than 10, no free. Store B: 15% off. Please be Mr. Xiao's "consultant", which store should I go to buy it? How much do you need?
肖老师要为学校买50个足球，现有两个商店可以选择．两个商店足球的标价都是50元，但各个商店的优惠方法不同．甲店：买10个赠送2个，不足10个不赠送．乙店：优惠15%．请你给肖老师当"参谋"，该去哪个商店购买？共需多少钱？
<gadget id="calculator">42 * 50</gadget>
<output>2_100</output>

<result>2_100</result>