The time it took car P to travel 600 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? Choose the correct choice:
A) 40 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 , ( 600 / x ) - ( 600 / ( x + 10 ) ) = 2 solving for x = 50 miles \ hr answer : b"
Answer: B