Do the inverse operation. Given is product, so look for the quotient which is the other factor.
The result: 9x² + 12xy + 16y² is a perfect trinomial which can be factored as(3x + 4y)².
Therefore, the other factor of number to be multipled to (3x-4y) is (3x + 4y)².
So that:(3x-4y) (3x+4y)² = 27x³ - 64y³