Zhang Ming walks 5 kilometers per hour, and Zhang Ming's father rides a bicycle 15 kilometers per hour. Zhang Ming's home is 8 kilometers away from the school. When Zhang Ming left school on Friday afternoon, his father rode a bicycle to pick him up. When his father picked up Zhang Ming, how many kilometers did Zhang Ming walk?
张明每小时步行5千米，张明爸爸每小时骑自行车行15千米．张明家离学校有8千米，周五下午张明从学校出发时，爸爸同时骑车去接张明，爸爸接到张明时，张明步行了多少千米．
<gadget id="calculator">5 + 15</gadget>
<output>20</output>

<gadget id="calculator">8 / 20</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(2/5) * 5</gadget>
<output>2</output>

<result>2</result>