and B go from city B to city A. A's speed is 5 km/h and B's speed is 4 km/h. When A started, B had already walked for 3 hours. A walks 10 kilometers and decides to move forward at a speed of 6 kilometers per hour. How many hours will A catch up with B?
甲、乙两人从B城去A城．甲速度为每小时5千米，乙速度为每小时4千米．甲出发时，乙已经先走了3个小时．甲走了10千米，决定以每小时6千米的速度前进．问几小时后甲追上乙？
<gadget id="calculator">3 * 4</gadget>
<output>12</output>

<gadget id="calculator">12 - 10</gadget>
<output>2</output>

<gadget id="calculator">10 / 5</gadget>
<output>2</output>

<gadget id="calculator">4 * 2</gadget>
<output>8</output>

<gadget id="calculator">2 + 8</gadget>
<output>10</output>

<gadget id="calculator">6 - 4</gadget>
<output>2</output>

<gadget id="calculator">10 / 2</gadget>
<output>5</output>

<result>5</result>