Your entry is correct other than a blank line (but the solver is ignoring the blank line).  Note that '9' is expressed as '3^2'.  The representation of a number by its prime factorization is standard with the software and its use can be viewed as a "best practice". For example, when working with fractions it is not immediately obvious that "91/28" has any cancellations at all, while the prime-factored version, "(7 * 13) / (2*2 * 7)", has an obvious cancellation of sevens.

Finally, clicking on a particular solution step allows you to review the logic which is employed: