x = O - 1

O, in the equation x = O -1, is either a variable or it is the character O.  

As a variable, to solve for x would simply be a simple restatement of the given:

            x = O -1 : x is a positive integer > 1

<o:p> </o:p>

In many computer programming languages, though, the uppercase O is an ASCII character represented by the decimal value of 79.  Subtracting 1 from this value gives the positive integer value 78.