It takes a teacher 55 minutes to drive 40 kilometers to the school every morning. One morning, she leaves home 7 minutes late, so how many kilometers per hour can she reach the school on time as usual?
某教师每天早上驾车40公里到学校需要用55分钟，某天早上她迟离开家7分钟，那么她的车速每小时为多少公里时才能和平常一样按时到达学校．
<gadget id="calculator">55 / 60</gadget>
<output>11/12 = around 0.916667</output>

<gadget id="calculator">7 / 60</gadget>
<output>7/60 = around 0.116667</output>

<gadget id="calculator">(11/12) - (7/60)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">40 / (4/5)</gadget>
<output>50</output>

<result>50</result>