The distance between A and B is 231 kilometers. A car drives from A to B to perform a task. It travels 56.4 kilometers per hour for the first 2.5 hours. Due to the urgency of the task, the rest of the journey must be completed within 1.5 hours. How many kilometers per hour should the average travel be?
甲乙两地相距231千米，一辆汽车从甲地开往乙地执行任务，前2.5时每时行56.4千米．由于任务紧急，余下的路程必须在1.5时之内完成，平均每时至少行驶多少千米？
<gadget id="calculator">2.5 * 56.4</gadget>
<output>141</output>

<gadget id="calculator">231 - 141</gadget>
<output>90</output>

<gadget id="calculator">90 / 1.5</gadget>
<output>60</output>

<result>60</result>