A and B are located on the same river, and B is 100 kilometers downstream of A. Ship A departs from A and ship B departs from B at the same time, and they head towards each other. When A arrives at B, and B returns to A immediately, the water speed is 2 m/s, and the still water speed of the two ships is the same. If the two encounters are separated by 20 km, find the speed in still water.
A、B两地位于同一条河上，B在A下游100千米．甲船从A，乙从B同时出发，相向而行，甲到B，乙到A立即返航，水速为2米/秒，且两船静水速度相同，如果两船两次相遇的地点相距20千米，求静水速度．
<gadget id="calculator">100 + 20</gadget>
<output>120</output>

<gadget id="calculator">120 / 2</gadget>
<output>60</output>

<gadget id="calculator">100 - 60</gadget>
<output>40</output>

<gadget id="calculator">120 / 2 / 40</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">(3/2) * 2</gadget>
<output>3</output>

<gadget id="calculator">2 + 3</gadget>
<output>5</output>

<gadget id="calculator">(3/2) - 1</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">5 / (1/2)</gadget>
<output>10</output>

<result>10</result>