Practice: A and B set off at the same time at AB, which is 12 kilometers apart, and walk in the same direction. A walks 4 kilometers per hour, the car is behind, and the speed per hour is 3 times that of A. How many hours later can B catch up with A?
练一练：甲乙两人在相距12千米的AB两地同时出发，同向而行．甲步行每小时行4千米，车在后面，每小时速度是甲的3倍．几小时后乙能追上甲？
<gadget id="calculator">4 * 3</gadget>
<output>12</output>

<gadget id="calculator">12 - 4</gadget>
<output>8</output>

<gadget id="calculator">12 / 8</gadget>
<output>3/2 = around 1.5</output>

<result>3/2 = around 1.5</result>