Xiao Ming is walking on the side of the road at a speed of 6km/h. A truck with a body length of 20m comes from behind at a constant speed. The time it takes to pass Xiao Ming is 1.5s. Find the speed of the car.
小明在公路边行走，速度是6km/h，一辆车身长20m的卡车从背后匀速驶来，经过小明身旁的时间是1.5s，求汽车行驶的速度．
<result>54</result>