A small river flows through towns A, B, and C. A steamboat travels between towns A and B, and the speed of the steamboat in still water is 11 kilometers per hour. There is a wooden boat ferry between towns B and C, and the speed of the wooden boat in still water is 3.5 kilometers per hour. It is known that the distance between A and C is 50 kilometers, and the water velocity is 1.5 kilometers per hour. A person goes down the river from town A to town B, and takes 1 hour to have lunch, and then goes down the river to town C, which takes 8 hours, so how many kilometers is the distance between towns A and B?
一条小河流过A、B、C三镇．A、B两镇间有汽船来往，汽船在静水中的速度为每小时11千米．B、C两镇间有木船摆渡，木船在静水中的速度为每小时3.5千米．已知A、C两地水路相距50千米，水流速度为每小时1.5千米．某人从A镇顺流而下去B镇，吃午饭用了1个小时，接着又顺流而下去C镇，共用8个小时，那么A、B两镇间的距离是多少千米．
<gadget id="calculator">3.5 + 1.5</gadget>
<output>5</output>

<gadget id="calculator">7 * 5</gadget>
<output>35</output>

<gadget id="calculator">50 - 35</gadget>
<output>15</output>

<gadget id="calculator">11 + 1.5</gadget>
<output>12.5</output>

<gadget id="calculator">12.5 - 5</gadget>
<output>7.5</output>

<gadget id="calculator">15 / 7.5</gadget>
<output>2</output>

<gadget id="calculator">2 * 12.5</gadget>
<output>25</output>

<result>25</result>