In the rectangular playground, the original length is 50 meters, and after expansion, the length increases by 50 meters, and the area increases by 3500 square meters compared with the original. How many meters is it to run around the original playground?
在长方形操场，原来长50米，扩建后长增加50米，面积比原来增加3500平方米．绕原操场跑一圈是多少米？
<gadget id="calculator">3_500 / 50</gadget>
<output>70</output>

<gadget id="calculator">50 + 70</gadget>
<output>120</output>

<gadget id="calculator">120 * 2</gadget>
<output>240</output>

<result>240</result>