Fred and Sam are standing 40 miles apart and they start walking in a straight line toward each other at the same time. If Fred walks at a constant speed of 4 miles per hour and Sam walks at a constant speed of 4 miles per hour, how many miles has Sam walked when they meet?	Choose one:
A) 5 B) 9 C) 20 D) 30 E) 45

Rationale: "relative distance = 40 miles relative speed = 4 + 4 = 8 miles per hour time taken = 40 / 8 = 5 hours distance travelled by sam = 4 * 5 = 20 miles = c"
Answer: C