Chen Shi and Zhang Jian rode bicycles from the same place in opposite directions at the same time. After 0.5 hours, the distance was 12.5 km. Chen Shi traveled 12 km per hour. How many kilometers per hour did Zhang Jian travel? (solution by equation)
陈实和张坚骑自行车从同一地点同时向相反的方向骑去，0.5小时后相距12.5km，陈实每小时行驶12km，张坚每小时行驶多少km？(用方程解)
<gadget id="calculator">12 * 0.5</gadget>
<output>6</output>

<gadget id="calculator">12.5 - 6</gadget>
<output>6.5</output>

<gadget id="calculator">6.5 / 0.5</gadget>
<output>13</output>

<result>13</result>