NDA Math Three Dimensional Geometry

(C)
Given equation of sphere is
x‌2 + y‌2 + z‌2 − 6 x + 8y − 10z+1 = 0
⇒ ( x‌2 − 6 x + 9) − 9 + ( y‌2 + 8 y + 16) − 16 + ( z‌2 − 10 z + 25) − 25 + 1 = 0
⇒ ( x−3)‌2 + ( y+4)‌2 + ( z−5)‌2 = 49
∴ Radius of given sphere = 7