You can't use a solve block that way. If you have multiple cases to solve for you have to turn the solve block into a function, and then apply the function to the multiple cases.
You have a more fundamental problem though. In the function Zz the units in the numerator and denominator are fundamentally incompatible. The numerator requires that Rp be unitless, whereas the denominator requires that Rp have the units of Ohms. So first, you need to fix the formula for Zz.