A car traveling at a certain constant speed takes 20 seconds longer to travel 1 kilometer than it would take to travel 1 kilometer at 36 kilometers per hour. At what speed, in kilometers per hour, is the car traveling? Choose the correct answer:
A) 24
B) 26
C) 28
D) 30
E) 32

Rationale: "36 * t = 1 km = > t = 1 / 36 km / h v * ( t + 20 / 3600 ) = 1 v ( 1 / 36 + 20 / 3600 ) = 1 v ( 120 / 3600 ) = 1 v = 30 km / h the answer is d ."
Answer: D