A and B start from two places 30 kilometers apart at the same time and walk toward each other. A walks 3.5 kilometers per hour and B walks 2.5 kilometers per hour. At the same time, at the same place, and in the same direction as A, there is a dog running 5 kilometers per hour. When the dog encounters B, it turns back and runs to A, and when it encounters A, it turns back and runs to B again... this dog Just go back and forth between A and B until they meet, how many kilometers did the dog run in total when they met?
甲、乙两人同时从相距30千米的两地出发，相向而行．甲每小时走3.5千米，乙每小时走2.5千米．与甲同时、同地、同向出发的还有一只狗，每小时跑5千米，狗碰到乙后就回头向甲跑去，碰到甲后又回头向乙跑去，…这只狗就这样往返于甲、乙之间直到二人相遇而止，则相遇时这只狗共跑了多少千米．
<gadget id="calculator">3.5 + 2.5</gadget>
<output>6</output>

<gadget id="calculator">30 / 6</gadget>
<output>5</output>

<gadget id="calculator">5 * 5</gadget>
<output>25</output>

<result>25</result>