Cars A and B drive towards each other from places A and B at the same time. Car A travels 75 kilometers per hour, and car B takes 7 hours to complete the journey. The distance between the two cars was 15 kilometers after driving for 3 hours (they did not meet). How many kilometers are there between A and B?
甲、乙两辆汽车同时从A、B两地相对开出，相向而行．甲车每小时行75千米，乙车行完全程需要7小时．两车开出3小时后相距15千米(未相遇)．A、B两地相距多少千米？
<gadget id="calculator">75 * 3</gadget>
<output>225</output>

<gadget id="calculator">225 + 15</gadget>
<output>240</output>

<gadget id="calculator">7 - 3</gadget>
<output>4</output>

<gadget id="calculator">240 / 4</gadget>
<output>60</output>

<gadget id="calculator">60 * 7</gadget>
<output>420</output>

<result>420</result>