It takes Zhang Hua 15 minutes to walk from home to school, and 5 minutes to ride a bicycle. He started from home by bike, but after 3 minutes the bike broke down and he changed to walk. How many minutes did he walk to the school?
张华从家到学校，步行需要15分钟，骑车需要5分钟．他从家骑车出发，3分钟后车子发生故障，改为步行，他到达学校步行了多少分钟？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/5) * 3</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(2/5) / (1/15)</gadget>
<output>6</output>

<result>6</result>