The distance between A and B is 100 kilometers. A and B travel from A to B. A walks 3 kilometers first, and then B starts again. As a result, B still arrives 1 hour earlier than A. It is known that B’s speed is 2.5 times that of A’s. Seek the speed of armor.
AB两地相距100千米，甲乙两人从A到B，甲先走3千米后，乙再出发，结果乙仍比甲早到1小时，己知：乙速是甲速度的2.5倍，求甲的速度．
<gadget id="calculator">250 - 100 - 7.5</gadget>
<output>142.5</output>

<gadget id="calculator">142.5 / 2.5</gadget>
<output>57</output>

<result>57</result>