How to calculate integer in base B

Since I am not a native English speaker and not a math whiz, I am left wondering how I even calculate the number that I am then supposed to check to see if it is a palindrome. Even after researching on the internet, I don't know how to do this.

A concrete example is missing in the description. The asserts do not help me here.

So please, can someone explain how to calculate the "integer in base B" number, whatever this is?