A test vehicle covered a 1 mile section in 1.5 min going against traffic and 2.5min going with traffic. Given that the traffic flow was 800 veh/h and that the test vehicle passed 10 more vehicles than passed it when going with traffic find (a) number of vehicles encountered by the test vehicle while moving against traffic, (b) the speed of th traffic being measured, (c) the concentration of the traffic stream, and (d) whether on its run with traffic the test vehicle was traveling faster or slower than the traffic stream.