A car traveling at a certain constant speed takes 2 seconds longer to travel 1 kilometer than it would take to travel 1 kilometer at 90 kilometers per hour. At what speed, in kilometers per hour, is the car traveling?  Choose the correct choice from the following answers
A) 71.5  B) 72  C) 72.5  D) 73  E) 85.7
Many approaches are possible, one of them:   Let the distance be 1 kilometer.   Time to cover this distance at 90 kilometers per hour is 1/90 hours = 3,600/90 seconds = 40 seconds;   Time to cover this distance at regular speed is 40+2= 
<gadget id="calculator">40+2</gadget>
<output>42</output>
42 seconds= 42/3,600 hours = 7/600 hours;   So, we get that to cover 1 kilometer 1/(7/600) hours is needed --&gt; regular speed 85.7 kilometers per hour (rate is a reciprocal of time or rate=distance/time).   Answer: 85.7.
<result>E</result>
A car traveling at a certain constant speed takes 2 seconds longer to travel 1 kilometer than it would take to travel 1 kilometer at 90 kilometers per hour. At what speed, in kilometers per hour, is the car traveling?