A rope with a length of 62.8dm is wrapped around the trunk of a big tree for a week and there is still 15.7dm left. What is the radius of the trunk of this big tree in dm?
用一根长62.8dm的绳子绕一棵大树的树干一周后还余15.7dm，这棵大树树干的半径是多少dm．
<gadget id="calculator">62.8 - 15.7</gadget>
<output>47.1</output>

<gadget id="calculator">47.1 / 3.14 / 2</gadget>
<output>7.5</output>

<result>7.5</result>