J.R. S. answered 10/20/19
Ph.D. University Professor with 10+ years Tutoring Experience
PbBr2(s) <===> Pb2+(aq) + 2Br-(aq)
Ksp = [Pb2+][Br-]2
[Pb2+] = 2.70x10-2
[Br-] = 2 x 2.70x10-2 = 5.40x10-2
Ksp = (2.70x10-2)(5.40x10-2)2
Ksp = 7.87x10-5 = 7.9x10-5