Ans 436
9647->multiply 1st & 4th digit &swap remaining digits=>4663
4663>multiply 2nd & 3rd digit &swap remaining digits=>3436
3436=>multiply 2nd & 4th digit & swap remaining digits.
3324=>multiply 1st & 3rd digit, swap remaining digits.=>436
However since selection of any such two digits can be done in 4C2 =>6 ways, there may be two more solutions, but appropriate selection seems to be by considering 1st & 3rd digit only.
