Yale School bought 3 water bottles and 20 teacups for the first time, with a total of 140 yuan, and bought the same 3 water bottles and 11 teacups for the second time, with a total of 104 yuan. How much does each water bottle cost?
雅乐学校第一次买了3个水瓶和20个茶杯，共用140元，第二次又买了同样的3个水瓶和11个茶杯，共用104元，每个水瓶要多少元．
<gadget id="calculator">140 - 104</gadget>
<output>36</output>

<gadget id="calculator">20 - 11</gadget>
<output>9</output>

<gadget id="calculator">36 / 9</gadget>
<output>4</output>

<gadget id="calculator">4 * 20</gadget>
<output>80</output>

<gadget id="calculator">140 - 80</gadget>
<output>60</output>

<gadget id="calculator">60 / 3</gadget>
<output>20</output>

<result>20</result>