The product of digits of a two digit number is 12.
That narrows it down to 26, 62, 34, or 43
when 9 is added to the number, the digits interchange their places.
26+9=35, 62+9=71, 34+9=43, 43+9=52
Only 34 interchanged the digits to 43 when 9 was added,
so the answer is 39
Edwin