There is a square with a side length of 12 cm. Two ants A and B start from the same vertex of the square and start in the same direction along the side of the square. The speed of two ants crawling per second is: A is 0.96 cm per second. B is 0.81 cm per second. How many seconds later, A began to see B's back.
有一正方形，边长12厘米，甲、乙两只蚂蚁从正方形的同一个顶点，沿着正方形的边同时同向出发．两只蚂蚁每秒爬行的速度是：甲为每秒0.96厘米．乙为每秒0.81厘米．多少秒钟后甲开始看见乙的后背．
<gadget id="calculator">0.96 - 0.81</gadget>
<output>0.15</output>

<gadget id="calculator">3 / 0.15</gadget>
<output>20</output>

<gadget id="calculator">12 * 20</gadget>
<output>240</output>

<gadget id="calculator">1 - 0.2</gadget>
<output>0.8</output>

<gadget id="calculator">12 / 0.96</gadget>
<output>12.5</output>

<gadget id="calculator">0.8 * 12.5</gadget>
<output>10</output>

<gadget id="calculator">240 + 10</gadget>
<output>250</output>

<result>250</result>