My original search on the i-net said it should be on the rear of the mower below the motor, but on my late 80'S model it was on the battery holder behind the seat. The first 2 digits are the size followed by the horsepower then an "x" , a series number and the last digit is for electric start. Mine is a 3012x6s 30", 12 hp, series 6, electric start.
Enjoy the ride