Xiao Ming's home is 2400 meters away from the school. At 17:00 Xiao Ming started to walk home from school, walking 40 meters per minute. His father also set off from home to pick up Xiaoming at 17:00, and picked up Xiaoming on the road at 17:20. How many meters does Xiao Ming's father have to walk to get home.
小明家离学校2400米．17：00小明开始从学校步行回家，每分钟走40米．他爸爸也在17：00从家里出发去接小明，17：20在路上接到小明．小明爸爸还要走多少米路才到家里．
<gadget id="calculator">40 * 20</gadget>
<output>800</output>

<gadget id="calculator">2_400 - 800</gadget>
<output>1_600</output>

<result>1_600</result>