The distance between A and B is 390km. A slow train travels from A to B. After driving for 1 hour, it is 45km away from A. At this time, an express train travels from B to A. After 3 hours, the express train travels to A. When the slow trains meet, find the speed of the express train.
甲、乙两地相距390km，一辆慢车从甲地开往乙地，开出1小时后离甲地45km，这时一辆快车从乙地开往甲地，快车开出3小时后，与慢车相遇，求快车的速度．
<gadget id="calculator">390 - 45</gadget>
<output>345</output>

<gadget id="calculator">345 / 3</gadget>
<output>115</output>

<gadget id="calculator">115 - 45</gadget>
<output>70</output>

<result>70</result>