The highway between A and B is 750 kilometers long. A car travels from A to B at a speed of 90 km/h. One hour later, another car drove from place B to place A at a speed of 75 kilometers per hour. How much time elapses before they meet after the second car starts?
甲乙两地的高速公路长750千米．一辆汽车以90千米的时速从甲地开往乙地．一小时后，另一辆汽车以75千米的时速从乙地开往甲地．在第二辆汽车出发后，经过多少时间它们才能相遇？
<gadget id="calculator">750 - 90</gadget>
<output>660</output>

<gadget id="calculator">90 + 75</gadget>
<output>165</output>

<gadget id="calculator">660 / 165</gadget>
<output>4</output>

<result>4</result>