Xiaojie goes up the mountain from A, crosses the top of the mountain and descends to B. He travels 2 kilometers per hour up the mountain and 5 kilometers per hour down the mountain. It takes 4.5 hours to travel from A to B, and 2.5 hours to return by the same route. Find the distance between A and B.
小杰从甲地上山越过山顶下山到乙地．他上山每小时行2千米，下山每小时行5千米，从甲地到乙地共用4.5小时，按原路返回用了2.5小时，求甲、乙两地之间的距离．
<gadget id="calculator">4.5 + 2.5</gadget>
<output>7</output>

<gadget id="calculator">5 + 2</gadget>
<output>7</output>

<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">7 * (5/7) * 2</gadget>
<output>10</output>

<result>10</result>