A store sells a drink, each bottle is a yuan, and Xiao Qiao bought 8 bottles of this drink for 50 yuan, how much should I get back.
商店里卖一种饮料，每瓶a元，小巧用50元钱买了8瓶这样的饮料，应找回多少元．
<gadget id="calculator">50 - 8</gadget>
<output>42</output>

<result>42</result>