Find the base K of the number system, if (524)8 = (664)K ?  Choose the correct choice:
A) 4  B) 5  C) 6  D) 7  E) 8
5*8^2 + 2*8^1 + 4*8^0 = 6*K^2 + 6*K^1 + 4*K^0   320 + 16 + 4 = 6(K^2) + 6K + 4   340 = 6(K^2) + 6K + 4   6(K^2) + 6K + 4 - 340 = 0   6(K^2) + 6K - 336 = 0   dividing by 6;   (K^2) + K - 56 = 0   solving this quadratic equation we get, K=7 and K=-8   thus K=7   ANSWER:7
<result>D</result>
Find the base K of the number system, if (524)8 = (664)K ?