Which value of x should the expression be further simplified?

Question

For which value of x should the expression be further simplified?   The square root of 21x.

     A. 5 B. 8 C.37 D.54.

Answer 1

21 is made up of factors 3 and 7. To make this into a perfect square, which would simplify the square root we would need to find a number for x containing an odd power of 3 (3, 27, etc.) or an odd power of 7. The best answer is 54=3^3*2. 21*54=3^4*2*7. So the square root is 9sqrt(14). Option D is the answer.

Answer 2

B=13