The distance between A and B is 465 kilometers. A car travels from A to B at a speed of 60 kilometers per hour. After a certain period of time, it accelerates at 15 kilometers per hour. It takes 7 hours to reach B. How many hours did you drive at 60 kilometers per hour?
甲、乙两地相距465千米，一辆汽车从甲地开往乙地，以每小时60千米的速度行驶一段后，每小时加速15千米，共用了7小时到达乙地．每小时60千米的速度行驶了多少小时？
<gadget id="calculator">60 * 7</gadget>
<output>420</output>

<gadget id="calculator">15 * 7</gadget>
<output>105</output>

<gadget id="calculator">105 - 465</gadget>
<output>-360</output>

<gadget id="calculator">420 + (-360)</gadget>
<output>60</output>

<gadget id="calculator">15 - 60</gadget>
<output>-45</output>

<gadget id="calculator">60 + (-45)</gadget>
<output>15</output>

<gadget id="calculator">60 / 15</gadget>
<output>4</output>

<result>4</result>