A car traveling at a certain constant speed takes 4 seconds longer to travel 1 km than it would take to travel 1 km at 80 km/hour. At what speed, in km/hr, is the car traveling? Select the correct option
A) 70 B) 72 C) 74 D) 75 E) 78
Time to cover 1 kilometer at 80 kilometers per hour is 1/80 hours = 3,600/80 seconds = 45 seconds;   Time to cover 1 kilometer at regular speed is  45 + 4= 
<gadget id="calculator"> 45 + 4</gadget>
<output>49</output>
49 seconds= 49/3,600 hours = 1/74 hours;   So, we get that to cover 1 kilometer 1/74 hours is needed --&gt; regular speed 74 kilometers per hour (rate is a reciprocal of time or rate=distance/time).   Answer: 74
<result>C</result>
A car traveling at a certain constant speed takes 4 seconds longer to travel 1 km than it would take to travel 1 km at 80 km/hour. At what speed, in km/hr, is the car traveling?