A is the average (arithmetic mean) of the first 7 positive multiples of 7 and B is the median of the first 3 positive multiples of positive integer n. If the value of A^2 – B^2 is zero, what is the value of n?  Choose the most appropriate option
A) 4 B) 12 C) 14 D) 21 E) 28

Rationale: "if a ^ 2 - b ^ 2 = 0 , then let ' s assume that a = b . a must equal the 4 th positive multiple of 4 , thus a = 28 , which also equals b . b is the second positive multiple of n , thus n = 28 / 2 = 14 . the answer is c ."
Answer: C