A and B are running a 100-meter race. When A reaches the finish line, B is 20 meters behind A. If both speeds remain the same, how many meters must A's starting line be moved back to make both A and B reach the finish line at the same time?
甲、乙两人百米赛跑，当甲到达终点时，乙在甲后面20米．如果两人速度都保持不变，要使甲、乙两人同时到达终点，甲的起跑线要后移多少米．
<gadget id="calculator">100 * 20</gadget>
<output>2_000</output>

<gadget id="calculator">100 * 100</gadget>
<output>10_000</output>

<gadget id="calculator">10_000 - 10_000</gadget>
<output>0</output>

<gadget id="calculator">2_000 + 0</gadget>
<output>2_000</output>

<gadget id="calculator">100 - 20</gadget>
<output>80</output>

<gadget id="calculator">2_000 / 80</gadget>
<output>25</output>

<result>25</result>