The time it took car P to travel 300 miles was 2 hours less than the time it took car R to travel the same distance. If car P’s average speed was 10 miles per hour greater than that of car R, what was car R’s average speed, in miles per hour?  Select:
A) 34 B) 50 C) 60 D) 70 E) 80

Rationale: "let speed of car r be = x then speed of car p = x + 10 a / q , ( 300 / x ) - ( 300 / ( x + 10 ) ) = 2 solving for x = 34 miles \ hr . a"
Answer: A