Xiao Zhang walks 5 kilometers per hour from A to B, and Xiao Wang walks 4 kilometers per hour from B to A. The two start at the same time, and then meet at a place 1 km away from the midpoint of A and B. Find the distance in kilometers between A and B.
小张从甲地到乙地，每小时步行5千米，小王从乙地到甲地，每小时步行4千米．两人同时出发，然后在离甲、乙两地的中点1千米的地方相遇，求甲、乙两地间的距离是多少千米．
<gadget id="calculator">5 + 4</gadget>
<output>9</output>

<gadget id="calculator">5 - 4</gadget>
<output>1</output>

<gadget id="calculator">2 / 1</gadget>
<output>2</output>

<gadget id="calculator">9 * 2</gadget>
<output>18</output>

<result>18</result>