A bus trip of 450 miles would have taken 1 hour less if the average speed S for the trip had been greater by 5 miles per hour. What was the average speed S, in miles per hour, for the trip?  Answers: A) 10 B) 40 C) 45 D) 50 E) 55

Rationale: "( s + 5 ) ( t - 1 ) = 450 s * t = 450 solving both the equations , we get : s = 45 or - 50 since speed should be positive , s = 45 hence , option c"
Answer: C