If a car had traveled 30 kmh faster than it actually did, the trip would have lasted 30 minutes less. If the car went exactly 90 km, at what speed did it travel? Choose one:
A) 35 kmh  B) 45 kmh  C) 60 kmh  D) 75 kmh  E) 90 kmh

Rationale: "time = distance / speed difference in time = 1 / 2 hrs 90 / x - 90 / ( x + 30 ) = 1 / 2 substitute the value of x from the options . - - > x = 60 - - > 90 / 60 - 90 / 90 = 3 / 2 - 1 = 1 / 2 answer : c"
Answer: C