The fast and slow trains start from opposite sides of the two cities at the same time, and meet at a distance of 18 kilometers from the midpoint after 4 hours. It is known that the fast train travels 70 kilometers per hour, how many kilometers per hour does the slow train travel?
快、慢两车同时从两城相向出发，4小时后在离中点18千米处相遇．已知快车每小时行70千米，慢车每小时行驶多少千米？
<gadget id="calculator">70 * 4</gadget>
<output>280</output>

<gadget id="calculator">18 * 2</gadget>
<output>36</output>

<gadget id="calculator">280 - 36</gadget>
<output>244</output>

<gadget id="calculator">244 / 4</gadget>
<output>61</output>

<result>61</result>