To solve this Arithmetic progression request, which requires a quite simple single line of code calculator I decided to make an universal calculator, which can derive remained parameters automatically from the input data and related formulas.
It's a little bit complicated, but powerful enough to automatically derive the solution form any formulas, containing arithmetic operations: +, -, /, * , ^.
Just enter input data and related formulas in the text field and get solution for remained unknown parameters.
The calculator recognizes two special constants - pi = 3.1415926... and e = 2.718....
If something fails to work as you expect it, just let me know in comments.