Two cars drove from Tangshan to Beijing at the same time, and after 1.5 hours, car B fell 30 kilometers behind car A. A car travels 90 kilometers per hour. How many kilometers does car B travel per hour?
两辆汽车同时从唐山开往北京，1.5小时后乙车落在甲车后面30千米．甲车每小时行驶90千米．乙车每小时行驶多少千米？
<gadget id="calculator">30 / 1.5</gadget>
<output>20</output>

<gadget id="calculator">90 - 20</gadget>
<output>70</output>

<result>70</result>