The distance between the two ports of A and B is 306 kilometers. After a cargo ship travels from A to B for 1.5 hours, a passenger ship travels from B to A. The cargo ship travels 42 kilometers per hour, and the passenger ship travels 39 kilometers per hour. Two ships meet? (Arithmetic first, then equational)
甲乙两港相距306千米，一艘货船从甲向乙行驶1.5小时后，一艘客船从乙向甲行驶，货船每小时行42千米，客船每小时行39千米，客船行驶几小时后两船相遇？(先用算术法，再用方程法)
<gadget id="calculator">42 * 1.5</gadget>
<output>63</output>

<gadget id="calculator">306 - 63</gadget>
<output>243</output>

<gadget id="calculator">42 + 39</gadget>
<output>81</output>

<gadget id="calculator">243 / 81</gadget>
<output>3</output>

<result>3</result>