A children's top is 50 yuan, a pair of trousers is 13 yuan cheaper than the top, and a skirt is 7 yuan less than the trousers. How much is this dress?
一件儿童上衣50元，一条长裤比上衣便宜13元，一条裙子又比长裤少7元．这条裙子多少钱？
<gadget id="calculator">50 - 13 - 7</gadget>
<output>30</output>

<result>30</result>