Zhang Dali and Wang Tao set off from point A on the ring road at the same time, ran in opposite directions, and met at point B for the first time. After Zhang Dali reached point B for the second time, he immediately turned around and ran in the opposite direction. It is known that it takes Zhang Dali 4 minutes to complete a lap, and Wang Tao 5 minutes to complete a lap. How long does it take for Zhang Dali to catch up with Wang Tao after turning around?
张大力和王涛从环形公路上的A点同时出发，沿相反方向跑，第一次相遇在B点．张大力第二次到达B点后立即掉头沿相反方向跑．已知张大力跑完一圈需4分钟，王涛跑完一圈需5分钟，请问张大力掉头之后经过多长时间追上王涛？
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/4) - (1/5)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(4/5) / (1/20)</gadget>
<output>16</output>

<result>16</result>