题目

I could clearly remember my first day in the 5th grade. I was a new student then, having transferred(转学) to a local school for boys. Life was really difficult for my parents having transferred me to a school with a higher schooling fee. As much as we could, all unnecessary expenses (费用) were dispensed with(免除). At school, we were required to wear a white shirt with the school’s sign on its upper left pocket that could be bought in the school shops. And at the top of this pocket a name tag(标签) should be worn to best prove each student. This tag was sold at the shops too.小明站在小亮的前面，两人同时同向起跑，小明的速度为4m/s，小亮的速度为6m/s，经过xs后小亮追上小明，起跑时小明站在小亮前面_________m.