Pool volume estimator
The first problem that jumps out at me is that many of your variables are "stringly typed".  This class is a calculator, right?  Why are you storing your numbers as strings rather than as doubles?

Why does the constructor take a num parameter, and what does it mean?

There is no need to redefine π.  Just use Math.PI.

Why is there a getPoolCost() method?  Your code would be more flexible if you offered a method to calculate the volume, and a separate method to calculate the cost based on the volume.

I don't think that there is much of a reason to define a bunch of setters and getters.  Just define one function that accepts all of the dimensions as parameters, and be done with it.