If 4^k = 5, then 4^(2k+2) = Pick one
A) 400 B) 540 C) 100 D) 830 E) 420

Rationale: "4 ^ k = 5 4 ^ 2 k = 5 ^ 2 4 ^ 2 k = 25 4 ^ ( 2 k + 2 ) = 4 ^ 2 k * 4 ^ 2 = 25 * 16 = 400 answer : a"
Answer: A