From Congcong to Hongxing Theater, it takes 30 minutes to walk. Later, I switched to go back and walk by car, which took 20 minutes. How many minutes did it take him to go by car?
聪聪去红星影剧院，如果来去都步行要30分钟．后来改用去时乘车回来步行，这样共用了20分钟．他去时乘车用了多少分钟？
<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">20 - 15</gadget>
<output>5</output>

<result>5</result>