Solving with multiple unknown variables & more

[Ollie]

Hey, I just recently got the HP Prime calculator and I have a few issues.
I want to solve, or "rearrange" an equation with multiple unknown variables.
Let's say I have an equation "x-a = 500" and solve for x I would get "x = 500+a".
Is there a way to do this on HP Prime or any symbolic calculator?

Another issue I'm having is how does one create custom functions and calculate their values at specific points.
Eg. I want to create a function f(x) = x^2+50, the get the derivative f'(x) and calculate f'(5).
I know you can do this with diff(x^2+50) but after that I'd have to copy the result into the where-block so I can get 2x | x=2 => 4.
There must be a simpler way to do this, right?