Xiaoqiang returned from the county town to his hometown in the countryside to visit his grandfather. For outings, he walked 4 kilometers per hour when he went there, and took a car when he returned to the county town, 20 kilometers per hour. Xiaoqiang spent 6 hours going back and forth. How many kilometers is it from the county seat to Xiaoqiang's rural hometown?
小强从县城回农村老家看望爷爷．为了踏青，去时步行，每小时行4千米，返回县城时乘车，每小时行20千米，小强往返共用6小时．县城到小强农村老家有多少千米？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/4) + (1/20)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">6 / (3/10)</gadget>
<output>20</output>

<result>20</result>