There are 50 frogs and ducks in a pond with 130 feet. How many frogs are there?
池塘里有青蛙和鸭子共50只，共有脚130只．青蛙有多少只．
<gadget id="calculator">50 * 4</gadget>
<output>200</output>

<gadget id="calculator">200 - 130</gadget>
<output>70</output>

<gadget id="calculator">4 - 2</gadget>
<output>2</output>

<gadget id="calculator">70 / 2</gadget>
<output>35</output>

<gadget id="calculator">50 - 35</gadget>
<output>15</output>

<result>15</result>