Two circles x2+y2=1x^2 + y^2 = 1x2+y2=1 and x2+y2−6x−8y+k=0x^2 + y^2 - 6x - 8y + k = 0x2+y2−6x−8y+k=0 are orthogonal. Find kkk.
999
161616
252525
000