A person bought a coat, a hat and a pair of shoes for 140 yuan. The coat is 90 yuan more expensive than the hat, and the coat and hat are 120 yuan more expensive than the shoes. How much is a pair of shoes.
一个人用140元买了一件外衣、一顶帽子和一双鞋．外衣比帽子贵90元，外衣和帽子共比鞋贵120元．一双鞋多少元．
<gadget id="calculator">140 - 120</gadget>
<output>20</output>

<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<result>10</result>