I am looking for a calculator where I could find the value of a missing variable within the Black Scholes formula. I came across this kind of calculator once on the Internet but I can't find it anymore.

E.G.

strike price 65

stock price 60

time (days) 30

volatilitiy (%) 20

option value 10 $

dividend yield(%) 0

What is the risk free interest rate (based on black scholes formula) ?

or

strike price 65

time (days) 30

volatilitiy (%) 20

option value 10 $

risk free interest rate(%) 2

dividend yield(%) 0

What is the stock price (based on black scholes formula)?

Basically, If I have 6 out of the 7 variables from Black Scholes formula, I want a calculator that would calculate the missing variable. Anyone here knows where I could find this?

Thank you for your help.