Ineed with 2 math questions evaluating subscripts

evaluate _[8]c_[4] and _[7]p_[4]

The ksp expression for the system pbcl2(s) pb+2(aq) + 2 cl-(aq) is: [pbc12][pb+2][2cl-] [pb+2][cl-]2 [pb+2][2cl-]2 [pbcl2][pb+2][cl-]2 [pb+2][2cl-]2[pbcl2]

Does anyone know how to do geometryme with this problem

Math each whole number with a rational,exponential expression